Peel the sweet potato, slice it and then cut it into eighths. Fry the pieces in the olive oil until they have turned some color. Meanwhile, clean and chop the spring onions. Fry the white of the spring onions. Pour in the vegetable stock and bring to the boil. Clean the garlic and cut into small cubes, add together with the tomatoes and season everything with salt and pepper. Simmer everything until the sweet potatoes are cooked through. Finally, melt the peanut cream in the sauce and season the dish with lemon juice.