Grilled Portobello Burger

6 large portobello mushroom caps
1/2 cup roasted garlic Teriyaki sauce, divided
6 (1-ounce) slices part-skim mozzarella cheese
1/4 cup mayonnaise
6 sourdough buns or rolls, split

1. Combine mushroom caps and teriyaki sauce in a heavy-duty zip-top plastic bag, turning to coat; seal and let stand 20 minutes.
2. Grill, covered with grill lid, over medium-high heat (350* to 400*F / 175*C to 205*C) 2 minutes on each side. Top with cheese, and grill 2 minutes.
3. Spread mayonnaise on cut sides of buns. Grill buns, cut sides down, 1 minute or until toasted. Place mushrooms in buns, and serve immediately.