Slit the wax gourds lengthways on 1 side and de-seed. To make the filling, put all the ingredients in a bowl and mix them together. Set aside.
Heat the oil in a kadhai, wok, or deep, heavy-based frying pan (skillet) to 180'C / 350'F, or until a cube of bread browns in 30 seconds.
Carefully add the wax gourds to the hot oil and deep-fry for about 2-3 minutes, or until half-done. Remove with a slotted spoon and drain on kitchen paper (paper towels). Reserve the oil. Stuff the wax gourds with the filling.
Heat 6 tablespoons of the reserved oil in a large, heavy-based pan over medium heat, add the cumin seeds and, stir-fry for 1 minute, or until they start to splutter.
Add the onion and stir-fry for about 5-7 minutes, or until golden brown. Add the ginger and garlic pastes and stir-fry for a further 2-3 minutes. Add the chilli powder and tomatoes and stir-fry for another 1-2 minutes, or until the oil separates out and rises to the surface.
Pour 125ml / 4 1/2fl oz (1/2 cup) water into the pan and bring to a boil. Add the stuffed wax gourds, then cover and simmer over low heat for 10-15 minutes, or until tender.
Sprinkle over the garam masala and the chopped coriander and stir, then remove from the heat.