Boil chicken breast for 10 minutes and shred with fork
Sauté onion, celery, and green pepper in ¼ cup butter/margarine
Add cream of celery soup and Rotell tomatoes
Cut Velveeta cheese into small pieces and add to mixture (the entire block will not melt well)
Cook on low for 20 minutes
Put shredded chicken breast into mixture
Cook spaghetti, serve