Measure the cumin, coriander, cardamom, fenugreek, cloves, cassia, peppercorns, mustard seeds, turmeric and sugar. Place in a dry frypan and heat to release the aroma and cook for a minute or two. Grind this up in a mortar and pestle with the vinegar, tamarind paste, chillies and garlic until fine.
Heat oil in a frypan and sauté the onions until fragrant and translucent. Add the spice paste and fry for a minute. Then add the tomato paste, 1 cup of water and potato. Simmer with the lid on for 10 minutes.
Then add in another cup of water and the sweet potato and simmer for 10 minutes with the lid on. Repeat with 1 cup water and 10 minutes for the eggplant and then lastly do the same for the green beans.
Season with salt and pepper and serve with basmati rice.