Step 1Slice chicken breasts into strips, and slice strips in half. Season with salt and pepper.
Step 2Heat oil in medium skillet over high heat. Add chicken and sprinkle with chili powder, lime juice and garlic. Cook until chicken is no longer pink inside, stirring occasionally, about 5 minutes.
Step 3Divide tortillas between 2 baking sheets. Spread each tortilla with 1/4 cup beans, 1/4 cup sliced avocado, 1/4 cup tomatoes and 1/2 cup cheese. Broil until cheese is melted and bubbly, 1 to 3 minutes.
Step 4Pour 2 tablespoons taco sauce over melted cheese on each burrito. Divide chicken among tortillas. Top with 1 to 2 tablespoons sour cream. Roll up tortillas by folding bottoms up 1/4 of the way, then sides so that they overlap each other.