1. Preheat oven to 475 degrees F.
2. Coat a baking dish with nonstick spray.
3. Cook spinach according to package directions; squeeze dry.
4. Combine the beans and 1 cup of salsa in a bowl.
5. Onto each tortilla, spoon one-fourth of the beans, spinach, cheese and sour cream (if using). Roll up.
6. Place tortillas seam side down in the baking dish.
7. Spoon the remaining salsa over the surface of the burritos and sprinkle with extra cheese if desired.
8. Bake until cheese is melted and burritos are heated through, 6 to 8 minutes.