Heat oil and mustard seeds in a medium saucepan over medium-high heat. Once seeds begin to pop, cover the pan and wait until the popping stops. Add cashews and yellow split peas; stir-fry until golden brown, about 30 seconds. Add onion and ginger; stir-fry until the onion is golden brown, 2 to 3 minutes.

Stir in water, potatoes, peas, chiles, salt and turmeric; bring to a boil. Reduce heat to medium-low, cover and simmer until the potatoes are tender, 5 to 6 minutes. Stir in wheat cereal; simmer, covered, until all the water is absorbed, 3 to 4 minutes. Stir in tomato and cilantro. Cover and simmer until the tomato is warm, 1 to 2 minutes. Serve.