Emeril's Favorite Pastrami Sandwich

Not sure this is as orgasmic as Sally's, but Emeril Lagasse swears by this one, so have what he's having.

6 ounces sliced pastrami
2 tablespoons whole-grain mustard
4 ounces beer
3 slices onion, rings intact
1 tablespoon oil
Salt and pepper
2 slices rye bread or thick crusty brown bread

Preheat a grill. Season onions with salt and pepper and brush with oil. In a small saucepan combine beer and mustard and bring to a boil. Add pastrami and simmer for 3 minutes. Grill onions on both sides and toast bread on a cooler part of the grill. When all ingredients are heated, prepare sandwich