Heat a medium pot on a medium heat. Peel and slice onions into rings. Cook onions in a little oil until they are soft and golden brown, about 10 minutes.
Add 2 cups water and bring to the boil. Simmer lentils uncovered for 20-25 minutes or until the lentils are no longer crunchy and the water has reduced. If the lentils start to dry out before they’re cooked, add more water.
Meanwhile combine tahini, lemon juice and 3-4 tablespoons water in a small bowl.
When the lentils are cooked season generously with salt and pepper. Toss in the parsley and serve with the tahini sauce drizzled over.