Lentils make an awesome meal, but can take a while to cook properly. By pressure cooking the lentils while you prepare onions and tomatoes, this half-an-hour dish will taste like it's been deliciously simmering for hours.
Dump a couple of cups of dry red lentils in a pressure cooker and cover with water. The best metric I've found is to cover them such that the water comes to a depth above the lentils equal to the distance from your finger tip to between the first and second knuckle.
Heat the water up and let it reach a boil, while stirring periodically to prevent the lentils on the bottom from burning. Seal the lid on, turn down the heat, and cook for 9 minutes at 8 psi. After 9 minutes, take the pressure cooker off the heat and either let it cool naturally, or vent it depending on how much volume you are cooking. If you have a larger volume, the lentils can overcook while they cool naturally.