Remove the dark stem end from 8 of the tomatoes. Carefully hollow out each tomato by removing the pulp and seeds; discard the seeds but save the pulp. Chop enough of the remaining 2 tomatoes, discarding the seeds, to make 1/4 cup together with the reserved pulp. Set aside.
Heat oil in a skillet over medium low heat. Sprinkle asafoetida over the oil. Fry onion until it is richly browned but not burnt, 8-10 minutes, stirring constantly. Add ginger, green chilli and turmeric and stir a few times. Stir in the besan. Lower the heat slightly. Add the reserved tomato pulp, salt and coriander. Cook until the pulp disintegrates into the sauce, about 2 minutes, stirring often. Transfer to a bowl and let cool slightly.
Stuff the hollowed tomatoes with this mixture and place upright in a baking pan. If they will not stand because of their point ends, place a crumpled piece of aluminium foil on the bottom of the baking pan and make small hollows in the foil to support the tomatoes upright. Or you can use a muffin pan.
Just before serving, preheat oven to 200C/390F. Bake the tomatoes until they are tender but retain their colour and shape, 7-12 minutes (the timing will vary with the firmness and size of the tomatoes). Do not over bake or the tomatoes will darken and their skin will wrinkle.
Serve immediately.