In a large saucepan, bring 1 in. of water to a boil; place squash in a steamer basket over water. Reduce heat; cover and steam for 10-15 minutes or until tender.
Meanwhile, in a large saucepan, saute onion and garlic in butter until tender. Stir in the salsa, salt and squash cubes. Spoon half of the mixture into a greased 1-qt. baking dish.
Sprinkle with 1/4 cup of cheese. Top with the remaining squash mixture.
Cover and bake at 400° for 15 minutes. Uncover; top with remaining cheese.