Steak Sandwiches

Steak Sandwiches
From Cooking Light magazine

Marinade:
1/2 cup dark rum
2 tablespoons brown sugar
1 tablespoon coarsely ground black pepper
1/4 teaspoon salt
5 garlic cloves, crushed, or 2 1/2 teaspoons bottled minced garlic
1 (1 1/2-pound) flank steak
Flavored mayonnaise:
1/2 cup fat-free or light mayonnaise
2 teaspoons prepared horseradish
Remaining ingredients:
8 (1/2-inch-thick) slices red onion (about 2 onions)
16 (1-ounce) slices sourdough bread
2 cups thinly sliced romaine lettuce
16 (1/4-inch-thick) slices tomato (about 3 tomatoes)

1. To prepare marinade, combine first 5 ingredients in a large zip-top plastic bag. Trim fat from steak, and add steak to bag. Seal and marinate in refrigerator at least 2 hours, turning bag occasionally. Remove the steak from bag, reserving marinade. Pour the marinade into a microwave-safe dish. Microwave marinade at HIGH 1 minute or until mixture boils.
2. To prepare flavored mayonnaise, combine mayonnaise and horseradish, and set aside.
3. Prepare grill. Place steak and red onion slices on a grill rack, and grill onions 4 minutes on each side, basting with the reserved marinade. Remove onions from grill.
4. Turn the steak, and grill an additional 8 minutes or until steak is desired degree of doneness. Remove steak from grill. Place bread slices on grill rack, and grill 2 minutes on each side or until toasted.
5. Cut steak diagonally across grain into thin slices. Spread 1 tablespoon flavored mayonnaise on one side of each of 8 toasted bread slices. Divide steak, onion slices, lettuce, and tomato slices evenly among 8 bread slices. Top with remaining bread slices.

Serves 8.

Substitute: pineapple juice for rum, if desired.