For red lentils, I use a recipe my mom got from her Indian friend. For two people with a little extra I use:
about a cup of red lentils
about 3 cups of water
a medium sized onion or a small bunch of spring onions, green parts included
a couple cloves of garlic
about a half tsp of turmeric
about half a tsp of mustard seeds
about a tsp of cumin
a pinch of cayenne (depending on how hot you want it)
a good tablespoon of olive oil
carrots and potatoes (just one or two of each)
salt to add at the end
First heat the oil on low and start the chopped onions sauteing. When they're a little tender add the mustard seeds, cumin and turmeric, then when the onions are almost done add the chopped garlic and cayenne. Let the garlic cook for a minute and then add the water, carrots and lentils. Bring to a boil and then turn down to simmer. When the lentils seem to be getting towards done (after about half an hour) add the chopped potatoes. When the potatoes and lentils are both all the way done, add salt to taste. If you have some fresh cilantro around, it's nice mixed in at the end, but totally optional.
You can eat this with rice but I prefer it just as a soup with some buttered toast.
For green/brown lentils my favorite light dish is very simple:
however many lentils you need
tomatoes (about 1 per person)
olive oil
salt
pepper
Cook the lentils however you normally cook them. When they are cooked and drained, put them back in the warm pot and add the chopped tomatoes. Mix them in and let them sit for a minute or two to get warm. Then add as much olive oil, salt and pepper as you like and eat. So simple but incredibly delicious.