Heat the oil in a pot over medium high heat until hot, then add the cumin, black mustard, and cloves. Fry the spices until they start to pop (be careful, the hot oil will spatter).
When the spices are popping and fragrant, add the garlic and ginger, stir frying until very fragrant (about 1 minute).
Add the onions, serrano chilies, and salt and fry over medium heat until the are translucent and starting to turn brown (20-30 minutes).
Add the bell peppers, zucchini, eggplant, tomatoes, garam masala and turmeric and stir to combine. Turn the heat down to medium low, cover and cook for 20 minutes covered.
Temove the lid and cook for another 10 minutes uncovered, or until the mixture is thickend to the texture you want.