Step 1

In a large skillet over medium-high heat, add the vegetable oil.

Step 2

Add the onions and the mushrooms to the hot oil and cook, while stirring well, until softened, about 2-3 minutes.

Step 3

Transfer the mushroom mixture to a small bowl and allow it to cool for 20 minutes.

Step 4

On a cutting board, lay out the chicken breasts.

Step 5

Season the chicken breasts evenly with 3 teaspoons of the black pepper, the salt, and the Italian seasoning, making sure to season them on both sides.

Step 6

Add the seasoned chicken breasts between two sheets of plastic wrap.

Step 7

Using a meat mallet or rolling pin, carefully flatten the chicken breasts to 1/4-inch thickness (about 6 inches wide).

Step 8

On a clean sheet of plastic wrap, add 1 of the flattened chicken breasts.

Step 9

Top the chicken breast on the plastic wrap with 1/3 of the spinach.

Step 10

Reserve 2 tablespoons of the mushroom mixture.

Step 11

Add 1/3 of the remaining mushroom mixture on top of the spinach layer on the chicken breast, spreading it out evenly and leaving a 1/2-inch border around the edges.

Step 12

Using the plastic wrap, tightly roll the chicken breast into a log and wrap it tightly in the plastic wrap. Twist the edges of the plastic wrap very tightly and use clips to secure the ends.

Step 13

Add 1 of the remaining flattened chicken breasts to a clean piece of plastic wrap. Top it with 1/2 of the remaining spinach and 1/2 of the remaining mushroom mixture. Using the plastic wrap, tightly roll the chicken breast into a log and wrap it tightly in the plastic wrap. Twist the edges of the plastic wrap very tightly and use clips to secure the ends.

Step 14

Add the remaining flattened chicken breast to a clean piece of plastic wrap. Top it with the remaining spinach and the remaining mushroom mixture. Using the plastic wrap, tightly roll the chicken breast into a log and wrap it tightly in the plastic wrap. Twist the edges of the plastic wrap very tightly and use clips to secure the ends.

Step 15

Place the rolled-up chicken breasts in the refrigerator for 30 minutes-1 hour.

Step 16

In a large, nonstick saucepan over medium, melt the butter.

Step 17

Add 1/3 cup of the parsley and the reserved mushroom mixture to the melted butter and cook, while stirring, until fragrant, about 2 minutes.

Step 18

Add the cream cheese and the garlic powder to the butter mixture and cook, while stirring well, until the cream cheese is melted, about 1 minute.

Step 19

Add the milk to the cream cheese mixture and stir well to combine.

Step 20

Add the parmesan cheese and the remaining black pepper to the sauce mixture and cook, while stirring, until the sauce begins to thicken.

Step 21

Cover the sauce and keep it warm.

Step 22

Preheat the oven to 375 degrees F.

Step 23

Transfer the stuffed chicken breasts from the refrigerator, remove the plastic wrap, and spray each with the cooking spray.

Step 24

Transfer the stuffed chicken breasts to a baking sheet.

Step 25

Roast the stuffed chicken breasts, rotating them about halfway through, until the chicken reaches an internal temperature of 165 degrees F, about 35 minutes.

Step 26

Transfer the baking sheet to a wire rack to cool for 5 minutes.

Step 27

Serve the chicken topped with the sauce and the extra parsley.