Combine mayonnaise, garlic powder and 1/4 teaspoon black pepper in small bowl; set aside. Cut focaccia into 6 pieces. Cut each piece in half horizontally; set aside. Combine turkey, oil, garlic, basil, salt and remaining 1/4 teaspoon black pepper in large resealable plastic food storage bag. Seal bag; knead to combine. Add bell pepper and zucchini; knead to coat.
Grill or broil turkey, bell pepper, and zucchini 4 inches from heat source 6 to 8 minutes on each side or until turkey is no longer pink in center. (Bell pepper and zucchini may take less time.) Top bottom half of each focaccia piece with mayonnaise mixture, tomatoes, bell pepper, zucchini and turkey. Top with focaccia tops.