Cook the sausages according to the pack instructions. Meanwhile, heat the olive oil in a pan and cook the mushrooms for 3-4 minutes until beginning to brown, then add the courgette and cook for 3 minutes. Add the tomatoes and passata to the pan, stir and cook for another 5 minutes, or until the tomatoes begin to burst.
Preheat the grill. Slice each sausage at an angle into 3 pieces and stir into the tomato mixture. Spoon into individual heatproof dishes (using slightly smaller ones for any children's portions). Sprinkle the cheese over each dish and grill for 4-5 minutes until bubbling. Cool slightly and serve with some bread, if you like.