Combine 3 teaspoons cornflour and cooking wine in a medium bowl, stir until smooth. Stir in 2 tablespoons soy and 2 teaspoons sugar. Add prawns. Stir to coat. Cover and refrigerate for 15 minutes if time permits.
Meanwhile, stir remaining 2 teaspoons cornflour with 1 tablespoon of the water in a small saucepan until smooth. Stir in the remaining water, remaining 1 tablespoon soy, 2 tablespoons sugar, pineapple juice, stock cube and tomato sauce. Bring to the boil, stirring constantly over medium-high heat. Remove from heat. Set aside.
Heat wok over high heat until hot. Drain any marinade from the prawns. Add 2 teaspoons oil to hot wok and swirl to coat the wok. Add half the prawns, stir-fry 30 seconds until golden. Remove to a plate. Repeat with remaining prawns.
Add remaining oil, Minicaps and green onions to the hot wok. Stir fry 1 minute. Return the prawns to the wok and pour over the sauce. Stir to coat. Add mango, stir to combine. Scatter over basil if using. Serve with rice.
TipTo save time you can use 1 cup of purchased sweet and sour sauce and approx 350g peeled green prawn meat.