Don't soak the lentils prior to cooking. Rinse them in a sieve with fresh water to remove any dust or debris. Lentils will approximately double in volume once cooked so you will need about ½ a cup of dried red lentils and ½ a cup of dried green lentils. Cover with plenty of water, bring to a boil, cover tightly, reduce heat to low and simmer until they are tender. For green lentils, cook time is usually about 15-20 minutes. For split red lentils, cook time is typically only about 5 minutes. Spoon a couple out and taste them to check done-ness periodically and as soon as they are ready, drain and leave to cool before using in the recipe. They can be cooked ahead and stored drained in the fridge for up to 3 days.