Clean, wash and dry zucchini and cut them into small cubes. Peel and halve onions and cut them into small cubes. Peel garlic and chop finely. Quarter peppers and remove seeds. Wash quarters, rub dry and cut into small cubes.
Heat the oil in a large pot. Fry the onions and garlic for about 2 minutes. Add bell peppers, zucchini and mustard seeds and, stirring occasionally, steam for another 10-12 minutes. Add vinegar, sugar, cumin and turmeric and stir in. Reduce heat and simmer for another 15 minutes. Coarsely puree the chutney with the chopping stick and season with salt and pepper.
Fill chutney still hot into glasses, close them and put them upside down for about 20 minutes.