Drain the rice from its soaking water. In the same saucepan, combine the par-cooked lentils, rice, 1 tablespoon cooking oil, salt, pepper, and coriander over medium-high heat. Cook for 3 minutes, stirring regularly.
Add enough warm water to cover the rice and lentil mixture by about 1 1/2 inches (this will likely be around 3 cups). Bring to a boil, letting the water reduce slightly. Then, cover the pot and cook until all the liquid has been absorbed and both the rice and lentils are well cooked through, about 20 minutes. Keep the pot covered and undisturbed for another 5 minutes.