Heat a tablespoon of olive oil in a pan and add sliced mushrooms and minced garlic. Toss the mushrooms on high heat for 2-3 minutes.

Add the Italian seasoning blend and ½ teaspoon salt. Cook for 2-3 minutes until the mushrooms are golden brown and slightly crispy around the edges. Remove them into a bowl and set aside.

To prepare the chicken breasts for stuffing, butterfly each breast (slice it in half almost all the way through, so it opens like a book with one edge intact).

Open each butterflied chicken breast. Sprinkle salt and black pepper on both sides. On one side, place a tablespoon or two of the cooked mushrooms, top with a handful of spinach leaves, and then sprinkle ¼ cup of grated mozzarella cheese. Fold the other side of the chicken breast over the filling and secure it with a toothpick to prevent the stuffing from coming out. Repeat for all chicken breasts.

Brush the remaining olive oil and melted butter evenly over both sides of the stuffed chicken breasts. Sprinkle with additional salt and black pepper.

Transfer the chicken breasts to the air fryer basket. Cook at 350°F (180°C) for 3-4 minutes on each side, adjusting based on thickness. Ensure internal temperature reaches 165°F (74°C). Remove to a plate and let rest for 2-3 minutes before serving.