Preheat oven to 350º F.
Heat vegetable oil in large skillet over medium-high heat. Add bell pepper, onion and garlic; cook, stirring occasionally, for 2 to 3 minutes or until vegetables are tender.
ADD chicken; cook, stirring frequently, for 3 to 5 minutes or until chicken is no longer pink. Stir in salsa and olives.
Place half of tortillas onto bottom of 9-inch-square baking dish. Top with half of chicken mixture and 1 cup cheese; repeat layers. Cover.
Bake for 20 to 25 minutes or until bubbly and cheese is melted. Serve with sour cream.