Combine taco sauce, sugar, vegetable oil and water in small bowl. Reserve 1/2 cup marinade mixture; cover and refrigerate.
Alternately thread beef, onions, zucchini, squash and bell pepper onto skewers. Place in 13 x 9-inch baking dish. Pour remaining marinade over kabobs. Cover; marinate in refrigerator for several hours or overnight, turning kabobs several times.
Grill or broil kabobs, turning and basting with reserved marinade, until beef is of desired doneness. Serve with Summer Salsa.
Servings: 6