Flank Steak and Caramelized Onions High Protein Meal Prep

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Now that all the holidays and visits home have wrapped up and I’m returning to real life, I wanted to carry a little bit of family back with me. This recipe came from my grandparents and was a regular in my family growing up and so always reminds me of home.

Flank Steak High Protein Meal Prep Close Up

In my family, we normally served this with mashed potatoes which are delicious with this meal but also extremely high-carb. As I prefer to limit my daily carbs and the marinade and onions have a good amount of carbs already, I left the mashed potatoes out of this meal prep. If you are not trying to limit carbs, I would definitely add them back in – they go perfectly together.

The flank steak with onions can also be served with any other vegetable but I do think the green beans make the best vegetable side. The firm texture holds up well refrigerated and reheated and the fresh crunch offsets the chewy umami of the steak and onions. Other great options would be broccoli, asparagus, peppers, or carrots.

Macros/Nutrition Facts

(For 1/6th of the full recipe below, including onions and green beans)

Calories539 kcal
Protein37 g
Carbs25 g
Fat32.5 g

As I’ve mentioned in previous recipes, it is commonly circulated that you can’t absorb more than 20g of protein per meal. This is a false claim and only applies to cases where you are consuming a modified, fast-absorbing protein like whey protein powder and not when you are consuming protein in its whole food form with other foods slowing the movement through the gut. If eating whole food proteins, you are able to absorb 0.4g of protein per pound of body weight in one meal.

One great way to slice a bunch of onions quickly is by halving or quartering the onions and then using the slicing blade in a food processor. Also minimizes the tears! See the food processor I use below:

Meal Prep Tools I Use and Love

Meal Prep Tools I Use and Love - glass prep containers, mason jars, dressing bottles, mixing bowls, food processor, dutch oven

1. Meal Prep Containers (PBA-free with microwave-safe lids!) | 2. 8 oz Mason Jars (perfect to bring along toppings like cheese, nuts, herbs, etc.) | 3. Sauce Bottles (just the right size and easy to clean) | 4. Mixing Bowl Set (the vertical sides make spills a thing of the past) | 5. Food Processor (worth investing the money – SO many uses and built to last) | 6. Dutch Oven (versatile, durable, and beautiful color)

Flank Steak High Protein Meal Prep Close Up

Flank Steak with Caramelized Onions and Green Beans High Protein Meal Prep

The savory, marinated steak simply melts in your mouth with a burst of sweet, carmelized onions on top. The green beans provide a refreshing crunch to the meal, making this a great balance of flavors and textures and coming in with a whopping 37g of protein per meal!
Course Main Course
Keyword beef, high protein, onions, steak
Prep Time 20 minutes
Cook Time 40 minutes
Marinating time 12 hours
Servings 6 meals


  • 2 lbs flank steak
  • 3 sweet onions


  • ½ cup canola oil
  • ½ cup balsamic vinegar
  • ½ cup soy sauce
  • ¼ cup brown sugar
  • 1 sprig fresh rosemary, finely chopped

Green beans

  • 1 ½ lb green beans
  • 2 tbsp butter
  • ½ tsp salt



  • Add all marinade ingredients to a 1 gallon ziplock bag.
  • Add flank steak to marinade in bag. Slice onions thinly and add to bag as well. Seal bag and turn several times to thoroughly coat steak and onions with marinade.
  • Marinate steak and onions in the refridgerator for 2-12 hours (up to 24 hours).

Cooking the Meal

  • When ready to cook, preheat grill to medium-high.
  • Remove the steak from the bag and set aside.
  • Place the entire remaining ingredients in the bag (the rest of the marinade and the onions) into a large skillet or dutch oven over medium heat. Sauté the onions, stirring frequently, until very tender, sweet, and carmelized. Place in medium bowl until dividing into containers.
  • When grill is heated, grill steak about 3-5 minutes per side to desired doneness. I prefer medium-rare but it depends highly on the thickness of the cut of meat. Use a meat thermometer for best results. Remove steak from grill once cooked on both sides and let rest for 5-10 minutes.
  • Meanwhile, cut greenbeans to desired length. Saute green beans along with butter and salt in a large skillet (can be done before or after the onions if you only have one skillet as I do). Cook for about 10 minutes with lid on, stirring frequently, to desired firmness.
  • Divide the green beans, steak, and onions equally into 6 containers.
  • Can be frozen but does best stored in refrigerator for up to 6 days. Reheat in microwave when ready to eat.
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