XXXIII: Pineapple Stuffed Burgers

1/4 c packed brown sugar
1/4 c ketchup
1 T prepared mustard
1/2 lb lean ground beef
2 slices unsweetened pineapple
1/8 t salt
1/8 t pepper
2 hamburger buns, split
2 lettuce leaves

In a small saucepan, combine brown sugar, ketchup and mustard. Cook over medium heat for 2-3 minutes, stirring occasionally. Meanwhile, shape beef into four patties. Place pineapple slices on two patties; top with remaining patties. Seal edges; sprinkle with salt and pepper.
Coat grill rack with nonstick cooking spray before starting the grill. Grill burgers, covered, over medium-hot heat for 7-9 minutes on each side or until meat is no longer pink. Serve on buns with the sauce and lettuce.

This is also from the Cooking for 2 recipe.