Mix turkey with minced onion, parsley, basil, and breadcrumbs. Mix in egg. Form into 12 meatballs—each about a rounded tablespoon.
Heat oil in a skillet. Brown meatballs evenly, about 5 minutes total. Pour tomatoes over meatballs and heat for about 5 minutes. Meatballs will be cooked through and tomatoes heated.
To serve: Put about 1 cup of squash on each plate and top with meatballs and sauce. Sprinkle with Monterey jack cheese and cilantro.