Soak skewers in water for 30 minutes; drain. Pour boiling water over the onions; let stand for 3 minutes; drain. Trim off root ends and gently press to slip off skins. Alternately thread onions, artichoke hearts, shrimp, and tortellini onto prepared skewer. Set on oiled vegetable grilling rack, if desired.
Grill for 6 to 8 minutes or until shrimp turn opaque, brushing frequently with Lemon-Tarragon Vinaigrette and turning once. To serve, place over radicchio or red Swiss chard leaves and pass Parmesan or Romano cheese, if desired. Makes 8 servings.
Stir together olive oil, lemon peel, lemon juice or dry vermouth, tarragon, garlic, crushed red pepper, salt; and pepper. Makes about 1/3 cup.