In large skillet, crumble ground beef and sausage. Add onion and cook, stirring, until meat is lightly browned or onion is softened, about 5 minutes. Pour off any fat and season with Tabasco and salt to taste. Set aside to cool. Spread refried beans in large (4 qt) shallow baking dish. Spread meat on top. Sprinkle chilies over meat. Toss together cheeses and arrange on top. Drizzle taco sauce over all in a decorative pattern. (Recipe may be made ahead of time to this point. Cover and refrigerate up to 24 hours. Let return to room temperature before baking.) Bake at 350 degrees for 20-30 minutes or until hot and bubbly. Remove from oven and immediately sprinkle with chopped scallions and sliced olives. Mound guacamole in the center. Top with sour cream, leaving some guacamole showing around the edges. Serve with tortilla chips for dipping.