Step 1: Preheat Oven
Set your oven to 375°F (190°C) to ensure proper cooking temperature while preparing the other components.

Step 2: Prepare the Stuffing
Slice jarred roasted red peppers into strips and roughly chop fresh baby spinach. Heat 1 tablespoon of olive oil in a skillet over medium-high heat. Add the spinach and cook until wilted, about 3 to 5 minutes. Stir in the roasted red peppers and minced garlic, cooking for an additional minute until fragrant. Season with salt and pepper, then transfer the mixture to a bowl and let it cool slightly. Mix in the slices of fresh mozzarella cheese to complete the stuffing.

Step 3: Prepare the Chicken
Pat the chicken breasts dry. Using a sharp knife, carefully cut a horizontal pocket about two-thirds into each breast, avoiding cutting all the way through. Season the chicken inside and out with salt and pepper. Lightly dredge each breast in the flour, shaking off any excess.

Step 4: Sear the Chicken
In a large oven-safe skillet, heat 1 tablespoon of olive oil and butter over medium-high heat until shimmering. Sear the chicken breasts for 2 to 3 minutes on each side until golden brown. Remove from the skillet and let them cool briefly.

Step 5: Stuff the Chicken
Open each chicken pocket and fill it generously with the roasted red pepper, spinach, and mozzarella mixture. Secure the openings with toothpicks if needed to keep the stuffing inside during baking.

Step 6: Bake
Place the stuffed chicken breasts back into the oven-safe skillet or transfer them to a baking dish. Bake in the preheated oven for 20 to 25 minutes, or until the internal temperature reaches 165°F (74°C).

Step 7: Rest and Serve
Remove the chicken from the oven and let it rest for 5 minutes to retain its juices. Carefully remove toothpicks before serving. Serve alongside healthy sides such as quinoa, steamed vegetables, or light pasta.