Preheat oven to 350°.
Place bread cubes in a single layer on a baking sheet. Bake at 350° for 12 minutes or until toasted. Set aside.
Brush tomato slices with 1 teaspoon olive oil, and sprinkle with 1/4 teaspoon salt and 1/4 teaspoon pepper. Place tomato slices on a foil-lined baking sheet. Broil 10 minutes on each side or until tomato slices are blackened. Combine 3 teaspoons olive oil, 1/4 teaspoon salt, 1/4 teaspoon pepper, tomato slices, parsley, and next 5 ingredients (parsley through garlic) in a food processor, and process until blended. Divide vinaigrette in half. Set aside.
Thread shrimp onto 6 (12-inch) skewers, and brush with half of vinaigrette. Prepare grill. Place kebabs on grill rack coated with cooking spray, and grill 4 minutes on each side or until shrimp are done. Remove shrimp from skewers. Combine remaining half of vinaigrette, toasted bread cubes, shrimp, lettuce, avocado, and sliced onion in a large bowl; toss gently to coat.