Take equal quantities of whole kalonji (black onion seed, or nigella), fenugreek, cumin, fennel and mustard seeds. How much you use depends on how spicy you like it, but I'd say maybe a quarter of a teaspoon of each.
Heat a bland oil (groundnut or sunflower, or ghee if you're feeling thin) until very hot, then add the spices and wait until they start popping. This is a dangerous phase, so stand well back and keep your safety goggles on! Then turn the heat down.
Next add half a large shallot or onion, and some pulped up garlic, green chilli and ginger (again, how much you add depends on your taste...I normally go for several chillis, 3 cloves of garlic and 1-2cm of ginger). Fry until transparent.
You can now add other vegetables to this...whatever you feel like. Tomatoes are normally good. Okra works if you like it. Oddly, I quite like sweet potato in it too.
While all this is going on, have a pan of red lentils simmering away (around 100-120g, methinks). Add to this half a teaspoon or turmeric and the other half of the shallot. If you're feeling spicy, you could also go for a couple of cardamon pods, a few cloves, some cinnamon, a couple of dried red chillis and a bay leaf or two.
Once the lentils are soft, mix all the veggies and the spices from the frying pan in with the lentils...