1. Bring 3 quarts water and 1 tablespoon salt to a boil in a large saucepan. Add pasta; cook for 8 minutes. Drain in a colander over a bowl, and reserve 1/3 cup cooking liquid.
2. Cook bacon in a large skillet over medium heat until crisp. Remove bacon from pan, reserving 2 teaspoons drippings in pan. Crumble bacon; set aside. Add butter to drippings in pan; cook 30 seconds or until butter melts. Increase heat to medium-high. Add squash; sauté 7 minutes or until almost tender. Add garlic; cook 1 minute, stirring constantly. Stir in remaining 1/4 teaspoon salt, pasta, reserved cooking liquid, and cheese; cook 2 minutes or until pasta is al dente, stirring frequently. Sprinkle with bacon and onions.