Preheat oven to 200°C/390°F (180°F fan).

Cut pockets into each chicken breast, being sure not to cut all the way through. Cut on the side with the fold in the meat, to keep the smooth side intact.

Season the inside and outside of the chicken with half the salt and pepper.

Melt butter in a heavy based oven proof skillet over high heat. Add mushrooms and cook for 3 minutes until they start to turn golden. Then add garlic, thyme, remaining salt and pepper and continue cooking for a further 2 minutes until mushrooms are golden.

Add baby spinach and stir until wilted – about 30 seconds.

Stuff mushroom mixture into the pocket of each chicken, then top with cheese.

Seal with toothpicks as best you can.

Wipe the pan with paper towels. Heat oil over medium high heat. Sear each side of the chicken breast for 1 ½ minutes until golden.

Transfer the skillet to the oven and bake for 15 minutes, or until the internal temperature of the chicken is 65°C/149°F.

Remove from tray, loosely cover with foil and rest for 5 minutes. Serve!