Peel and finely chop the onions. Peel the sweet and regular potatoes and chop them into chunks around 2cm across. Peel and thickly slice the carrots.
Warm a big pan or casserole dish over a medium heat for 2 mins. Add the oil and the onions. Season with a pinch of salt and pepper. Cook for 5 mins, stirring now and then, till the onions start to soften.
While the onions cook, slice off the green top of the aubergine and chop the rest into bite-size chunks. Peel and crush or grate the garlic. Drain and rinse the lentils.
Stir the garlic into the pan with the curry powder. Cook and stir for 1 min. Add the rest of the veg and the lentils. Crumble in the stock cube and pour in 1 ltr boiling water.
Put the lid on the pan and bring to the boil, then turn the heat down and simmer for 30 mins till the veg are tender. While the hotpot cooks, roughly chop the herbs.
Taste the hotpot and add more salt or pepper if you think it needs it. Stir in the herbs and ladle into bowls to serve.