Heat oven to 375°. In a skillet, sauté peppers and onion in oil until tender. Stir in picante sauce; set aside. Cook frozen vegetables according to package directions; drain. Cool slightly; coarsely chop. Place two tortillas side by side on an ungreased baking sheet. Spread each with ¹⁄³ cup refried beans and sprinkle with ¹⁄³ cup of the pepper mixture. Top each with another tortilla. Spoon 1½ cups vegetables over each tortilla and sprinkle with Monterey Jack cheese. Top the last two tortillas with remaining beans and pepper mixture; place one on each stack. Sprinkle with cheddar cheese. Bake for 10 to 15 minutes or until heated through and cheese is melted. Garnish with cilantro and olives. Cut into wedges. Serve with sour cream and picante sauce. Yields two stacks and 4 to 6 servings.