Preheat oven to 350°.
Heat a large nonstick skillet coated with cooking spray over medium-high heat. Add onion, and sauté 3 minutes or until tender. Add beans and next 4 ingredients; cook 5 minutes or until mixture thickens. Remove from heat; cover and keep warm.
Coat each side of tortillas lightly with cooking spray. Place on a baking sheet, overlapping if necessary. Bake at 350° for 4 minutes on each side or until lightly browned.
Place 2 tortillas, slightly overlapping, on each of 4 plates. Top evenly with beans, lettuce, cheese, picante sauce, and sour cream.