Combine onion, celery, garlic, parsley and butter in 2 to 2 1/2-quart casserole.
Microwave 3 to 4 minutes on HIGH, or until onion is transparent.
Add tomatoes, sauce, oregano, salt and pepper.
Microwave 10 minutes on HIGH, or until bubbly, stirring after 5 minutes.
Add crab meat.
Microwave 1 to 2 minutes on HIGH, or until crab meat is hot.
Serve over cooked spaghetti, sprinkle with parmesan cheese.