Soak 3 dozen 4-inch long wooden skewers in water overnight. Place pearl onions and enough water to cover them in a 1-quart saucepan over high heat. Bring to a boil; reduce heat to low, cover, and simmer 3 minutes or until onions are tender. Drain. Peel away outer layer of skin when onions are cool enough to handle.
Combine olive oil, balsamic vinegar, TABASCO® Sauce, basil, garlic, and salt in a medium bowl. Pour half of mixture into another bowl. Cut chicken and beef into 3/4-inch chunks and place in a bowl with TABASCO® Sauce mixture, tossing to coat well. Toss cooked pearl onions, red and green peppers and zucchini in remaining bowl of TABASCO® Sauce mixture. Let stand at least 30 minutes, tossing occasionally.
Preheat grill to medium-high. Skewer one chunk of chicken or beef and one each of red pepper, green pepper, onion, and zucchini onto each wooden pick. Grill 4 to 6 minutes or until chicken and beef are done, turning occasionally.
Makes 6 to 8 main dish servings, or 18 appetizer servings.