In a bowl, combine the coriander with the cumin, peppercorns, turmeric and 1/4 teaspoon of the salt. Add the chicken and rub with the spices to coat. Cover with plastic wrap and let stand at room temperature for 20 to 30 minutes.
In a large deep nonstick skillet, heat 1/4 cup of the oil. Add the onions and cook over moderately high heat, stirring occasionally, until golden, about 8 minutes. Add the chicken, garlic, ginger, serrano chile and the remaining 3/4 teaspoon of salt and cook, stirring occasionally, until the chicken is golden brown and just cooked through, about 10 minutes. Stir in 1/4 cup of the coconut milk and the water, then cover and cook over low heat for 20 minutes.
Meanwhile, in a small skillet, heat the remaining 2 tablespoons of oil. Add the cashews and cook over moderate heat, stirring constantly, until golden brown, 4 to 5 minutes. Drain on paper towels.
Add the remaining 1/2 cup of coconut milk and the lemon juice to the chicken and simmer, stirring. Transfer to a bowl, sprinkle with the cashews; serve hot.
Choose an aromatic, fruity (but not sugary) whiteperhaps a Riesling from Washington State.