In a large skillet or wok heat the olive oil over medium high heat. Add the onions and sauté until soft and slightly brown, about 3 minutes. Add the chicken, cooking until browned on all sides.
Add the beer, scraping to deglaze the pan.
Lower the heat, add the coconut milk, curry paste, fish sauce, lime juice and cayenne pepper. Simmer until thickened, about 10 minutes.
Serve over rice or rice noodles, garnish with cilantro and peanuts just prior to serving.