Heat 1 tbsp olive oil in a large skillet over medium heat. Add red onion and bell pepper and sauté for about 5 minutes, until tender.
Add 1 cup of baby spinach to the pan and cook for a minute, until it is lightly wilted. Remove vegetables from heat and set aside into a large bowl.
In a separate large bowl, add 10 large eggs and 1/3 cup milk. Whisk until well combined.
Heat remaining 1 tbsp olive oil (or spray pan with cooking spray) in same skillet you used for the veggies. Add the eggs and cook over medium heat, periodically stirring to make scrambled eggs.
When eggs are done, remove from heat and add them to the bowl with the veggies.
Slice the breakfast sausage into bite size pieces and put into a bowl (note – since this one used fully cooked sausage and you’ll be heating it up later, you don’t have to pre-cook it. But you certainly can toss it in the microwave now for a minute if you’d like. If you bought uncooked sausage, please cook it first according to package directions in the skillet!).
Set up your burrito building station – set out the egg/veggie mixture bowl, the bowl of breakfast sausage, the cheese, and your tortillas. To each tortilla, add a scoop of egg/veggie mixture, a few bite size pieces of sausage, and sprinkle some cheese on top.
Roll the tortillas up and wrap each individually in plastic wrap. Then place them all in one freezer bag.
To reheat, place a tortilla on a plate and cover with a damp paper towel. Cook in the microwave for about 1:30 to 2 minutes, or until heated through.