Place tomato puree in a measuring cup. Add enough water to make a total amount of 1 cup, place in a medium bowl. Stir in cream, ginger, cayenne pepper, lemon juice, cumin, 1 teaspoon salt, black pepper to taste and sugar. Cover and refrigerate until needed.
Heat oil in a large frying pan over a medium-high heat. Add the mustard seeds. As soon as they begin to pop, add the garlic. Stir once and add the prawns. Stir and fry until they just turn opaque, sprinkling with salt and pepper to taste.
Pour in the pink sauce and stir. As soon as the sauce is bubbling, the dish is ready to be served with hot cooked pasta or rice.