Clean the aubergines by removing most of the stalk. Leave a small part of stalk to enable you to hold the aubergine. Make a cross cut on the fleshy side and leave them submerged in a pan of water.
Keeping the skin of new potatoes make a slit on the long side of each potato. Soak the slit potatoes in a bowl of warm salted water. This will help in the stuffing process.
Skin all the onions and slit similar to the potatoes.
Skin the sweet potatoes(if using) and again slit them on the longer side.
Finely grind the peanuts and transfer to a big bowl.
Add ginger, chilies, garlic and finely chopped spring onions.
Add the rest of the stuffing ingredients and mix to form a paste. To get the right consistency either add a little more oil or more ground peanuts and dhana/jeeru. Adjust seasoning as required.
Remove the potatoes and aubergine from the water and squeeze out all the water. Stuff all the vegetables with the stuffing, keeping them all separate.
Heat the oil in a large preferably non-stick pan, and add mustard, cumin, fenugreek seeds and turmeric.
When the seeds start to splutter add the asafoetida powder and place the aubergines in the pan. Toss so that the aubergines are coated with the oil. Reduce heat, cover and cook for 5 minutes.
Add the potatoes and the rest of the vegetables. Again cover and cook for a further 5 minutes.
Toss the pan so that all the vegetables get a coat of oil. You can also use a spatula for this, but be very gentle. Try not to dislodge the stuffing from the vegetables. Cover again and cook on a low heat. If vegetables start sticking to the bottom of the pan add a quarter cup water. Do not add too much water.
Carefully turn the vegetables over occasionally so they can cook evenly, making sure that the ingredients do not become mushy and the vegetables stay intact.
Chop the tomatoes and place them in the same container in which the stuffed uncooked vegetables were kept. This way the remainder of the stuffing can be used up and also add flavour to the dish.
Using a fork or a skewer check to ensure all the vegetables are cooked thoroughly. Should the vegetables be still hard, then transfer to a microwave proof vessel and cook in the microwave for 3 minutes at a time until all the vegetables are cooked.
Add the tomatoes and 2-3 spoonfuls of water to create some gravy. Cover and cook for a few minutes more. Add 1 tsp of sugar if required.
Transfer to a new container, garnish with chopped coriander and grated coconut.