2⁄3 cup mayonnaise
Zest from 1 medium lemon
2 teaspoons fresh lemon juice
1 garlic clove, pressed (about 1 teaspoon)
1 yellow squash
1 medium zucchini
1 medium eggplant
1 medium red or sweet yellow onion
Olive oil for brushing
Freshly ground black pepper
1 (12-ounce) loaf focaccia bread
8 ounces sliced mozzarella or provolone cheese
1 (6-ounce) jar roasted red peppers (drained), or 2–3 tomatoes, sliced
1 cup loosely packed basil leaves
1. Stir together mayonnaise, lemon zest, lemon juice, and garlic. Place in an airtight container in the refrigerator until ready to use. Can be prepared a day ahead of time.
2. Preheat outdoor grill or indoor grill pan to about 400 degrees F. Line a large baking sheet with foil. Slice squash and zucchini into 1⁄4-inch slices on a slight diagonal. Slice eggplant and onion into 1⁄4-inch slices. Place sliced vegetables on baking sheet in a single layer and brush lightly with oil. Sprinkle lightly with salt and pepper. Grill vegetables in batches, 3–4 minutes on each side, or until tender and showing grill marks.
3. While vegetables are grilling, slice the entire focaccia loaf in half horizontally and spread lemon-garlic mayonnaise on each side. Layer sliced cheese on each side of bread. As warm veggies come off the grill, place them directly on the bottom half of the focaccia. Top with roasted red peppers or tomatoes and basil leaves. If desired, place top half of focaccia under broiler to melt the cheese and then place on top of sandwich. Serve warm or at room temperature.