California Grilled Veggie Sandwich

INGREDIENTS

• 1/4 cup mayonnaise
• 3 cloves garlic, minced
• 1 tablespoon lemon juice
• 1/8 cup olive oil
• 1 cup sliced red bell peppers
• 1 small zucchini, sliced
• 1 red onion, sliced
• 1 small yellow squash, sliced
• 2 (4-x6-inch) focaccia bread pieces, split horizontally
• 1/2 cup crumbled feta cheese