Heat olive oil in a large non-stick skillet over medium heat.
Add diced onion and red bell pepper to the skillet and sauté for 3-4 minutes until softened.
Add chopped spinach and cook for an additional 1-2 minutes until wilted.
In a medium bowl, whisk together the egg whites, salt, and black pepper.
Pour the egg whites into the skillet with the vegetables and cook, stirring gently, until eggs are fully set, about 3-4 minutes.
Remove the skillet from heat and stir in the cooked turkey sausage.
Warm the tortillas in the microwave for 10 seconds to make them pliable.
Divide the egg mixture evenly among the tortillas, placing it in the center of each.
Sprinkle about 1 tablespoon of shredded cheddar cheese over the egg mixture on each tortilla.
Fold in the sides of each tortilla and then roll tightly to form burritos.
Wrap each burrito individually in plastic wrap or aluminum foil and place them in a freezer-safe container or bag.
To reheat, remove the wrapping and microwave each burrito on high for 1-2 minutes or until heated through.