Pre-heat the oven to 410F/210C.
Use a large sharp knife to (carefully) slice each chicken breast in half across the width so that it's no more than roughly 2cm thick. Place in a medium to large baking dish. Sprinkle generously all over with salt and pepper.
Pile the feta cheese (crumbled) onto the 4 chicken breast halves. Sprinkle with the dried oregano, then drizzle over the olive oil and lemon juice.
Bake the chicken for around 17 minutes, or until the inside is 165F/74C. If you don't have a meat thermometer, it's ready when the inside is white in the thickest part and the juices run clear.
