Heat oil in medium saucepan over medium-high heat. Add onions; cook until soft and translucent, about 7 minutes. Stir in jalapeno pepper, garlic and cumin; cook until fragrant, about 30 seconds more. Add beans and their liquid to saucepan; bring bean mixture to a boil. Using potato masher, submersion blender or fork, mash beans until broken. Cook, stirring constantly until mixture is thick, about 5 minutes.
To assemble burritos, mound ½ cup rice, ½ cups bean mixture, ¼ cup cheese, 2 tbsp. corn, 1 tbsp. chopped scallions and 1 tsp. cilantro on one side of tortilla. Roll up tortilla into burrito shape (see below). Place burrito, seam-side down on serving plate or platter. Repeat with remaining ingredients.
Serve burritos with guacamole, pico de gallo, salista and sour cream, if desired.
For a neat, leak-proof burrito, try this rolling technique: After arranging the ingredients on the tortilla, fold in the left and right ends. Then, holding the closed ends, fold tortilla in half from bottom to top. Using the top layer of tortilla, push filling towards you to compact. Roll tortilla into log and place seam-side down on platter.