In a bowl, stir together water, tomato sauce, soya sauce, corn flour, honey, chilli and ground ginger. Set aside.
Heat oil in a wok or frypan over medium-high heat. Stir in shallots and garlic; cook 30 seconds. Stir in the prawns and toss to coat with oil. Stir in sauce. Cook and stir until sauce is bubbly and thickened.