Heat the oil in a large skillet over high heat; heat the curry paste in the oil about 30 seconds.
Add the chicken and cook another 3 minutes.
Stir in the onion, bell pepper, lemon zest, coconut milk, fish sauce, and lemon juice; bring to a boil; cook until the chicken is cooked through, 5 to 7 minutes.
Sprinkle cilantro over the dish; stir.
Serve hot.
