Heat the oil in a large nonstick skillet over medium-high heat. Add the bell pepper and cook, stirring frequently, until tender, about 5 minutes. Add the chicken, cumin, and chili powder and cook until the chicken is no longer pink, 4 to 5 minutes. Stir in the beans, corn, cheese, and salsa and cook until the mixture is heated through and the cheese is melted, about 2 minutes. Meanwhile, stack the tortillas on a microwave-safe plate, uncovered, and heat in the microwave until warmed through, 30 to 45 seconds. Assemble by placing the chicken mixture down the center of each tortilla. Wrap burrito style and serve with sour cream as desired.