Thaw scallops, if frozen. Fold a 36x18-inch piece of heavy foil in half to make an 18-inch square. Place squash and carrots in center of foil. Sprinkle lightly with salt and pepper. Bring up 2 opposite edges of foil; seal with a double fold. Fold remaining edges to completely enclose vegetables, leaving space for steam to build.
Grill packets on the rack of an uncovered grill directly over medium heat for 15 to 20 minutes or until vegetables are crisp-tender, turning occasionally.
For sauce, stir together sweet-and-sour sauce, basil, Thai seasoning, and garlic in a bowl. Set aside 1/4 cup for basting. Reserve remaining sauce until ready to serve.
Thread scallops onto four 8- to 10-inch skewers, 1/8 inch apart. Place kabobs on grill rack next to vegetables the last 5 to 8 minutes of grilling or until scallops are opaque, turning and brushing once with basting sauce halfway through cooking. Pass remaining sauce. Makes 4 servings.