Combine olive oil, soy sauce, and tempeh. Let stand 20 minutes. Add 1/4 cup barbecue sauce; toss. Thread tempeh, mushrooms, grape tomatoes, and 16 bell pepper alternately onto skewers. Place skewers on a grill rack coated with cooking spray. Grill 9 minutes or until browned, turning skewers occasionally for an even char. Sprinkle with chopped green onions. Serve with barbecue sauce.
Note: If using wooden skewers, soak them in water for 20 minutes before grilling.