Grilled Portobello Burgers

INGREDIENTS

• 2 Tbs. olive oil
• 1 Tbs. balsamic vinegar
• 1 garlic clove, minced
• 1/2 tsp. salt, plus more, to taste
• 1/8 tsp. freshly ground pepper, plus more, to taste
• 4 large portobello mushrooms, stems removed
• 4 slices Monterey Jack or smoked mozzarella cheese
• 4 round Italian rolls
• 2 Tbs. purchased pesto
• 1/2 cup mayonnaise
• 1 to 2 tomatoes, sliced