Microwave squash for 2 minutes. Peel and dice to yield about 2 pounds.
Heat oil in large skillet on medium for 2 minutes. Add onion, and cook about 2 minutes. Turn heat to medium-high, add beef and cook until brown, about 4-6 minutes.
Place mixture in slow cooker. Add remaining ingredients. Cover, cook on low 5 to 6 hours.