Heat oil in a large pot over medium heat. Add peppercorns, cinnamon stick, cloves, cumin seeds, green cardamom, and black cardamom; cook and stir until starting to sputter, 30 seconds to 1 minute.
Stir onion into the pot; cook until translucent, about 5 minutes. Add garlic paste, ginger paste, and water; cook until fragrant, about 1 minute. Add potato; cook and stir until slightly softened, about 3 minutes. Stir in tomato; cook until juices start to evaporate, about 2 minutes.
Pour water into the pot; add green chile pepper. Bring to a boil. Pour in rice; cook until rice comes up to the surface of the water, 5 to 10 minutes. Cover and simmer over low heat until rice is tender and water is absorbed, 10 to 15 minutes more.
