Preheat the oven to 350 degrees F (175 degrees C). Bring a large pot of lightly salted water to a boil. Add pasta, and cook for 8 to 10 minutes, or until al dente.
In a large skillet over medium heat, cook ground beef and onion until beef is no longer pink. Drain grease, and stir in the chili, cream of mushroom soup, evaporated milk, mushrooms and black olives. Mix in 3/4 of the Cheddar cheese and the cooked shell pasta. Transfer the mixture to a 9x13 inch baking dish, and sprinkle remaining cheese over the top.
Bake for 1 hour in the preheated oven, or until the top is browned and bubbly.