Method:
Prepare grill for medium-high-heat cooking. Drizzle bell peppers, eggplant and zucchini with 2 teaspoons oil and sprinkle with 1/2 teaspoon salt. Grill the vegetables, turning frequently, until browned and tender, about 8 minutes. Set aside. Brush bread slices on both sides with 1 teaspoon oil and grill until browned, about 1 minute on each side. Split one garlic cloves and use it to rub bread slices all over; discard garlic. Cut grilled bread into cubes and set aside.
Meanwhile, finely chop remaining garlic clove and place it in a large bowl. Add lemon juice, mayonnaise, anchovies (if using), pepper, remaining 2 tablespoons oil and remaining 1/4 teaspoon salt to bowl and whisk until combined. Whisk in Parmesan. Add lettuce and toss until combined. Chop vegetables into bite-size pieces and toss with lettuce. Sprinkle salad with remaining 1 tablespoon Parmesan and croutons.