Mercimek koftesi, a vegetarian version of meatballs (kofte), is one of the most popular appetizers in Turkish cuisine. They are served as a meze with tzatziki or tahini sauce for dipping, or as is with lettuce leaves and a squeeze of lemon juice.
In a saucepan, combine the lentils and 2 cups (16 fl oz/475 ml) water and bring to a boil over medium heat. Cook until almost all the water has been absorbed and the lentils are tender, about 30 minutes.
Meanwhile, in a separate saucepan, combine the millet with water to cover. Bring to a boil over medium heat, then cover and simmer until softened, about 10 minutes.
Drain the millet, add to the lentils pot, and season with the salt. Cover with a lid to let the millet soak up the excess lentil cooking water.
In a frying pan, heat the olive oil over medium heat. Add the onion and stir-fry until soft, about 5 minutes. Stir in the tomato paste (tomato puree) and cook for 2 minutes. Remove from the heat and stir in the cumin.
Add the onion mixture to the lentils/millet mixture. Mix in the lemon juice, half of the parsley, and half of the scallions (spring onions).
Prepare the lentil balls by taking a tablespoon of the lentil mixture in your hands and rolling it into an oval shape. Wet your hands frequently as the mixture will make them sticky. Line a platter with the lettuce leaves.
Gently place the lentil balls on top of the leaves. Sprinkle with the remaining parsley and scallions. Keep the dish in the fridge until serving time.