Commenting on my post about lentils, Will Skidelsky said that he had never succeeded in making the perfect dhal. I do not think that I have, either; but I have been reasonably happy with my imperfect versions. The secret of happiness is not to allow one's enjoyment to be spoiled by an awareness of the gulf between the food on one's plate and anything that might be considered authentic.
You have to cook the red lentils -- or perhaps yellow ones (which are not really lentils), or the pulse sometimes known as mung dhal -- in a covered pan with enough water or stock to soften them, but then uncover the pan to allow the contents to thicken. They start to collapse after 10 to 15 minutes.
I follow roughly the formula I use for a vegetable curry. Allowing 200 g lentils for a substantial main course for two people (it would provide a side dish for four), I simmer them with 1/2 teaspoon turmeric, 1/3 tsp chilli powder or cayenne pepper, and 40 g creamed coconut. Meanwhile, I fry two onions in a sunflower/groundnut oil and butter mix, with 1 clove chopped garlic. I warm 1/2 tsp of cumin seeds and 1/2 tsp of coriander seeds in a dry pan until they give off a toasted aroma, and crush them in a mortar with five cardamom pods. When the onions are brown (there is more about browning onions here), I add the spices to them, along with a small amount of minced ginger, and cook them for a minute. I stir the spicy onions into the lentils, which I like to have the consistency of lava, and serve.
Fresh, chopped coriander and chillis are a nice garnish. Some people like toasted almond flakes.
These are the ingredients I am most likely to have available. Another option is a soupy Thai one, with a can of coconut milk, nam pla, shallots, lemon grass, lime leaves, lime juice, ginger, fresh coriander, and fresh chillis. You make a paste with the shallots, lemon grass, lime leaves, lime juice and ginger; and you fry it. You add it to the lentils, which you have simmered with the coconut milk, some stock, and nam pla.