Steam potatoes until tender. Mash well with margarine and milk. Season to taste and keep warm.
Heat oil in a heavy-based pan on medium heat. Cook garlic, onion and carrot for 5 min, until tender. Add lentils and tomatoes. Cook for 10 min, until the sauce thickens.
Spoon lentil mixture into a 6-cup overproof dish and top with mashed potatoes. Press haloumi slices into the mash. Bake in oven for 20-25 min, until golden on top.
