Put the onion into a very large bowl with the oil and place it in the microwave. Cook on full power for 4 minutes until the onions start to brown. Add the cardamoms, fenugreek, mustard, coriander seeds and turmeric. Cook on full power for 1 minute, stirring halfway through cooking. Add the diced potato to the mixture and cook on full power for 3 minutes, stirring twice. Add the courgettes, cauliflower florets, beans, tomatoes and bay leaves, cover and cook on full power for 5 minutes. Add about half the water. Cover and cook for 10 minutes. Reduce the setting to defrost/low and cook for 15 minutes, stirring occasionally, until the vegetables are tender, adding the remaining water if necessary. Adjust seasoning to taste.