Ok My girlfriend Mathilde is a vegetarian. That's why I've learnt to cook a lot of non meat meals.
Lentils I think have a bad name because of them being the food of the character Neil in the popular 80's comedy serial The Young Ones. Lentils I think have been portrayed as a tasteless gruel for vegans and hippies when they are in fact quite tasty. They're also a lot easier to cook than you think.
I've used red and green lentils and they both have their uses. The green ones are a bit heavier and meatier though.
I normally fry some diced onion with whatever vegetables I have to hand. Pepper, mushroom and courgette this time. Then add the lentils (give them a rinsewash first). Then I add a tin or two of tomatoes and cover everything with stock. If you then simmer it all everything should cook in under 35 minutes.
I normally add bay leaves, garlic and oregano and eat it with rice but if you add a little bit of mint to the mixture it's perfect as the filling for a vegetarian mousaka.