Brown beef and crumble in a large skillet. Add onions and cook until transluce nt. Season to taste with salt and pepper. Spread refried beans in the bottom of an 11/13 inch baking dish; top with meat mixture. Sprinkle chiles, then che eses, then taco sauce over all. Bake at 400�F for 20 minutes. Remove from oven and sprinkle green onions and olives over all. Mound mashed avocado in the ce nter; top with sour cream. Serve with chips.