Peel garlic and ginger and press them through a garlic press and add them to the ketchup. Drain the pineapple. Collect the juice and stir into the ketchup sauce with the lime juice. Season to taste with salt and pepper.
Carefully rub the mushrooms with kitchen paper. Cut off the hard stems. Rinse sprouts and basil cold and drain well. Cut pineapple slices into small pieces. Rinse shrimps in cold water and dab dry.
Heat oil in a wok. Fry the mushrooms for about 8 minutes, turning them over. After 4 minutes add the prawns. Season with salt and pepper. Fold in pineapple, sprouts and sauce. Fry for the last 3 minutes, turning gently.
Fold in basil leaves.