Slice bell peppers into 1 – 2in. stalks and set aside.
Slice flank steak against the grain, then slice into smaller, more bite-sized slices.
Cook 1 cup raw quinoa with 2 cups broth for about 15 minutes or until the quinoa has absorbed all the liquid and become semi-translucent. Remove from heat when finished.
Heat a cast iron skillet, add cooking oil, and sauté the bell peppers until browned or charred. Set bell peppers aside.
Reheat cast iron skillet (if needed) to searing temperature and add steak strips. Flip and rearrange steak strips as needed while they cook and release juices.
Once the steak strips are reasonably cooked, set aside on a paper towel lined plate, and pour the juices out of the skillet. Give the skillet a good wipe down, then return to heat and add some more oil.
Pat steak strips dry before returning them to the skillet. Flip and rearrange as needed until the steak strips have a crispy browned outside, fajita-style. Set aside when finished.
Rinse and drain two 15oz. cans of black beans.
In a mixing bowl, add cooked quinoa, black beans, bell peppers, steak strips, and Pico de Gallo. Mix until everything’s evenly distributed.
Serve in bowls with avocado slices and (optionally) grated cotija cheese and a spoon of sour cream. Or, use as filling for a burrito.