Preheat oven to 200 degrees. Spray a casserole dish large enough to fit tortillas. Heat olive oil in pan and cook onion and capsicum for 5 minutes, until softened. Mix in chili powder, remove from heat, stir in black beans and corn.
In a medium bowl, mix salsa and sour cream.
Layer tortilla, salsa mixture, chicken, tortilla, vegetables, cheeses. Repeat 4 times, or until you reach the top of the casserole. Top with cheese. Cover and bake for 25 minutes. Uncover and bake 10-15 minutes longer or until cheese is bubbly and browning. Let stand for 10 minutes before serving. Sprinkle with a little salt and pepper or herbs to taste.