Bring 1 litre of water and salt to the boil in a saucepan. Heat the fat in a pan. Fry the prawns in it for 4-5 minutes without defrosting them while turning them and take them out. Fry deep-frozen vegetables in a pan over high heat for 3-4 minutes, then over medium heat for about 4 minutes. Sprinkle rice into boiling salted water and cook for about 10 minutes. Stir the vegetable stock, tomato ketchup and soy sauce into the vegetables and simmer for 1-2 minutes.
Season to taste with some salt and cayenne pepper. Place the prawns on the vegetables and warm them up. Put rice on a sieve and drain. Divide into 4 plates. Arrange the Chinese vegetables and prawns on top