1) Combine sugar, vinegar and ginger in a small pot and bring to a boil, dissolve sugar and turn off heat, reserve.
2) In a skillet heat the oil over medium-high heat. Saute the onions, chili peppers, mushrooms and garlic 3 to 4 minutes then add prawn and toss 3 to 4 minutes more until pink and firm. Douse the pan with the sweet vinegar, season with salt and pepper, to taste. Serve with cold lettuce for wrapping the hot-sweet prawn.