Pat the chicken dry and carefully slice a pocket into the side of each breast, ensuring not to cut all the way through. Season inside and outside with salt and pepper.

In a skillet, heat butter with a little olive oil. Add mushrooms and cook until they shrink and most of the moisture is gone. Add garlic and cook for about 30 seconds.

Toss in fresh spinach and cook just until wilted. Turn off the heat and stir in cream cheese and parmesan until it forms a creamy mixture. If it's too thick, add a tiny splash of cream or milk.

Spoon the filling into each chicken pocket, securing with toothpicks if necessary.

Heat a bit of oil in an oven-safe skillet. Sear the stuffed chicken for about 2 to 3 minutes per side until golden.

Move the skillet to a preheated oven at 400°F and bake until the chicken reaches 165°F in the thickest part.