1Heat oven to 400°F. Spray 9-inch springform pan with cooking spray. Using bottom of pan as a guide, trim tortillas to fit inside pan.
2In 12-inch skillet, heat oil over medium heat. Cook onion, bell pepper and garlic in oil 5 to 7 minutes, stirring occasionally, until tender. Stir in corn, black beans and kidney beans. Cook 2 minutes longer. Add taco sauce; stir until vegetables are coated. Season with salt and pepper. Remove from heat.
3Place 1 tortilla in bottom of springform pan; sprinkle with 1/4 cup of the cheese. Top with one-third of the bean mixture; sprinkle with another 1/4 cup cheese. Repeat layers twice. Top with fourth tortilla and remaining 1/2 cup cheese.
4Bake 20 to 25 minutes or until thoroughly heated and cheese is melted. Let stand 5 minutes. Sprinkle with cilantro and green onions. Carefully remove side of pan. Cut stack into wedges. Serve with guacamole and sour cream.