In a medium bowl, whisk together the eggs, whole milk, ground cumin, smoked paprika, salt, and black pepper until well combined.
Heat olive oil in a large non-stick skillet over medium heat.
Add diced red bell pepper, green bell pepper, and red onion to the skillet. Cook, stirring occasionally, until the vegetables are softened, about 5 minutes.
Add chopped spinach and cook for an additional 1-2 minutes until wilted.
Pour the egg mixture into the skillet with the vegetables. Stir gently and cook until the eggs are fully scrambled and cooked through, about 4-5 minutes.
Remove the skillet from heat and stir in the black beans and half of the shredded cheddar cheese until the cheese is melted and evenly distributed.
Warm the flour tortillas in the microwave for about 15 seconds to make them pliable.
Divide the egg and veggie mixture evenly among the tortillas, placing it in the center of each.
Sprinkle the remaining shredded cheddar cheese on top of the filling in each tortilla.
Fold in the sides of each tortilla and then roll tightly from one end to the other to form burritos.
Wrap each burrito tightly in plastic wrap or aluminum foil.
Place the wrapped burritos in a large freezer-safe bag or container and freeze for up to 3 months.
To reheat, unwrap a burrito and microwave on high for 2-3 minutes or until heated through. Alternatively, reheat in a 350°F (175°C) oven wrapped in foil for 20-25 minutes.
Serve with salsa if desired.