1 cup chopped onion, about 1 large onion
2 tablespoons oil
1/2 cup tomato sauce
1/2 cup water
1 tablespoon brown sugar
1 tablespoon vinegar
1/2 teaspoon salt
1/8 teaspoon ground black pepper
dash ground cayenne pepper
2 cups cubed roast leftover lamb

Sauté onion in skillet over medium heat in oil until softened. Add tomato sauce, water, brown sugar, vinegar, salt, and black and cayenne peppers. Cook mixture over medium heat for 5 minutes. Add leftover lamb; cover and simmer for 15 to 20 minutes. Serve barbecued lamb over hot cooked rice or mashed potatoes.
Barbecued leftover lamb serves 4.

Source: http://southernfood.about.com