Wash squash thoroughly and place in a steamer basket. Place steamer basket in a saucepan filled with 1 inch of water. Bring water to a boil. Cover pan and steam 5 minutes or until tender but firm.
Drain and cool slightly. Trim off stems. Cut squash in half lengthwise; scrape out pulp (set aside for later use), leaving a firm shell.
Coarsely chop the pulp and set aside.
Cook ground turkey, onion, and green pepper in a large skillet until browned, stirring to crumble. Drain.
Stir in squash pulp and tomatoes.
Place squash shells in a baking dish and spoon ground turkey mixture into shells.
Bake at 350℉ for 25-30 minutes, or until squash is tender but firm. Sprinkle with cheese and bake 5 more minutes, or until cheese melts.