Preheat the oven to 350 degrees F. Grease a 9-by-13-by-2-inch baking dish with cooking spray.
In a large skillet, cook the bacon until slightly crisp. With a slotted spoon, transfer the bacon to a paper-towel-lined plate to drain. Saute the garlic, onion and bell pepper in the bacon drippings until tender. Add the tomatoes, olives, oregano, bacon and the cooked ground beef and simmer, uncovered, for 10 minutes.
Place half of the spaghetti in the prepared baking dish; top with half of the vegetable-beef mixture; and sprinkle with 1 cup of the cheddar. Repeat the layers. In a bowl, stir together the cream of mushroom soup and 1/4 cup water until smooth, and pour this over the casserole. Sprinkle with the Parmesan and bake, uncovered, for 30 to 35 minutes, or until heated through.