In a large, nonstick skillet, heat the olive oil over medium heat. Add the red bell pepper and onion, and season to taste with salt and pepper. Cook, stirring occasionally, for 5 minutes, or until the vegetables begin to soften.
Meanwhile, in a large bowl, combine the eggs, milk, salsa, hot sauce (if using), and a pinch of salt and pepper. Whisk until smooth.
When the vegetables have softened, turn the heat to low and add the egg mixture to the skillet. Cook, stirring constantly, until the eggs have cooked through, about 3 minutes.
Add 1 cup of cheddar cheese and the black beans and cook for 1–2 more minutes, or until the cheese has melted. Remove the egg mixture from the heat and let it cool slightly.
Once the eggs have cooled, place a tortilla on a clean, dry surface. Add about 1 ½ cups of the egg mixture to the center of the tortilla. Starting at the bottom, fold the tortilla up and over the eggs, tucking the sides of the tortilla in as you roll. When there's one or two inches of tortilla remaining at the top, sprinkle about 1 tablespoon of the remaining grated cheese, then continue rolling so the seam with the cheese is on the bottom of your surface. Repeat with the remaining egg mixture and tortillas.
Spray a large nonstick skillet with cooking spray, then set it over medium heat. Working with two burritos at a time, place them seam-side down in the hot pan and cook for 1–2 minutes, or until the bottoms are deeply golden brown. Remove from the heat and repeat with the remaining burritos.
Cut in half and serve immediately.