Balsamic Chicken with Pears

Prepare breasts by butterflying them three to four times (making them very thin). Cut one large red onion or two shallots into chunks. Cut 2 bosc pears without seeds in quarters. Put all into bowl. Mix in 1 cup of balsamic vinegar. Let rest 10 minutes. Grill on aluminum foil on BBQ. Serve on crusty bread, add roasted red pepper, and two slices provolone cheese.