Slice the top fifth off the tomatoes. Carefully scoop their insides out, turning the seeds and cores into a bowl. Arrange the tomato shells in a shallow baking or pie dish.
In a medium frying pan, heat the oil. Stir in the onion, fenugreek and coriander seeds and cook slowly for 5 minutes. Add the garlic and continue to cook until the onions are pale gold, 7–8 minutes. Add the mushrooms