Pat the chicken breasts dry with kitchen paper. If they’re very thick, slice them in half horizontally or place between two sheets of cling film and gently pound to about 2cm thick.
In a small bowl, mix together the salt, freshly ground black pepper, garlic powder and onion powder, then season both sides of the chicken evenly.
Heat the olive oil in a large frying pan over a medium–high heat. When it’s shimmering, add the chicken and cook for 5–7 minutes on each side, until golden and a meat thermometer inserted into the thickest part reads 74°C.
Transfer the chicken to a plate and loosely cover with foil. Reduce the heat to medium–low, add the butter to the pan and let it melt. Stir in the lemon juice and zest, scraping up any browned bits, then simmer for 1 minute.
Return the chicken to the pan, turning it in the lemon pepper sauce to coat. Scatter over the parsley and serve.