Heat oil in a small saucepan over medium-high heat. Add cumin seeds and peppercorns to pan. Cook 30 seconds or until cumin turns reddish brown, stirring constantly. Transfer to a mortar; let cool. Crush cumin mixture with a pestle until coarsely ground.
Rinse lentils in a sieve under cold running water until water runs clear. Combine lentils, 4 cups water, and rice in a large saucepan; bring to a boil. Stir in cumin mixture, salt, and turmeric; cook 5 minutes, stirring occasionally. Cover, reduce heat to low, and cook 10 minutes, stirring once. Remove from heat and let stand, covered, 10 minutes. Stir in cilantro and remaining ingredients. Serve immediately.