Grilled Chicken Sandwich with Roasted Red Onion and Garlic Mayonnaise

Source: Cuisine Magazine - July/August 1997

Serving size: 6

Garlic Mayonnaise
3 slices red onion (1/2-inch slices), roasted
1 head garlic, roasted
2 tablespoons olive oil

Sandwich
1 loaf focaccia bread, sliced
1/2 cup olive oil, for marinade
2 boneless chicken breast halves, grilled and sliced
5 portobello mushrooms, grilled and sliced
1 1/2 tablespoons olive oil, for saut