Slice the zucchini, leek, onion, bell pepper and lemon, cut tomatoes in half, chop the garlic. Transfer all vegetables to a baking tray, lined with foil.
Cut the fish into bite-sized pieces and add to the vegetables. Add salt and pepper, drizzle with oil and add pieces of butter around evenly.
Fold the foil and make sure you folded the foil well at joints.
Bake for 35-40 minutes and serve. Can be served with aioli or any other low carb sauce of your choice.