I make a warm salad with them.
Rinse the lentils, then cook in simmering water (no salt to be added) until they are tender - around 15-20 minutes, but keep checking after about 10 minutes. Sometimes they cook more quickly than others.
When they are tender, drain.
While the lentils are cooking, saute a large onion, chopped along with a large carrot, cut into small dice, a couple of rashers of smoked bacon, also diced and some garlic (amount up to you) in a large frying pan, in olive oil. You can add chilli if you like - again, amount up to you. I also add dried oregano.
When it's all softened (and the carrot has to be softened, so it needs to cook for a reasonable amount of time), add the drained lentils. Stir it all together, season with sea salt and black pepper and add another sloosh of olive oil and a bit of wine vinegar. Serve warm.