In a medium bow, mix together all the sauce ingredients.
Heat the oil in a skillet over medium heat, then add the onion and sauté for a few minutes until the onion softens and begins to brown. Now add the lentils and the sauce. Cover and bring to a gentle simmer until the lentils are cooked and tender, and most of the liquid is absorbed, about 8 to 10 minutes.
Serve by spooning over rice, and garnishing with the green onions and sesame seeds.