1. Cook rice according to package instructions; set aside.
2. Meanwhile, heat oil in a large saucepan over medium. Add onions, garlic, jalapeño, and cumin; season with salt and pepper. Cook, stirring occasionally, until golden, 10 to 12 minutes. Add tomato paste, and cook, stirring, 1 minute.
3. Add beans and 1 ½ cups water; bring to a boil, reduce heat to medium, and simmer, stirring occasionally, until thickened, 10 to 12 minutes. Add corn; cook to heat through, 2 to 3 minutes. Remove from heat; stir in scallions.
4. Heat tortillas according to package instructions; fill with rice, bean mixture, and cheese.
5. Assemble: Mound ¼ cup rice, ¾ cup bean mixture, and ¼ cup cheese on one side of tortilla. Fold, and hold in sides. Starting from filled end, holding sides in as you work, tightly roll into a bundle. Place on a baking sheet, seam side down, and prepare remaining burritos.
6. Serve immediately, with salsa and sour cream, if using, or wrap individually in plastic and freeze up to 3 months.
7. Reheating From Frozen:
8. Microwave and oven: Remove frozen burritos from plastic wrap. Place on a microwave-safe plate; microwave on high for 3 minutes. Transfer to baking sheet; bake at 450° until crispy, about 10 minutes. This is our favorite quick method.
9. Oven only: Remove frozen burritos from plastic wrap; rewrap individually in aluminum foil. Place on a baking sheet; bake at 450°, 40 minutes; remove foil, and bake to crisp, 5 to 10 minutes. (To reheat defrosted burritos, remove any wrapping, and bake for 10 minutes.)
10. Microwave only: Remove frozen burritos from plastic wrap. Place on a microwave-safe plate, covered with a microwave-safe bowl, and defrost at high power for 3 to 4 minutes; uncover, and microwave on high, 3 to 4 minutes longer.