Prep the oven and pan: Preheat your oven to 400°F (200°C). Lightly grease a baking dish or line a sheet pan with parchment.

Flatten or slice the chicken: Pat chicken dry. Either butterfly each breast by slicing horizontally to create a pocket, or pound to 1/2-inch thickness between two sheets of plastic wrap. Thinner chicken cooks more evenly.

Season the chicken: Sprinkle both sides with salt, pepper, paprika, and half the Italian seasoning. Drizzle with a little olive oil and rub it in.

Make the filling: In a bowl, mix softened cream cheese, shredded cheese, garlic, green onions, lemon zest, spinach (if using), a pinch of salt, pepper, and the remaining Italian seasoning. Stir until smooth and well combined.

Stuff the chicken: Spoon the filling into the pocket of each breast, or spread over half of each pounded piece and fold it over. Do not overfill. Secure the edges with toothpicks to keep the filling inside.

Optional quick sear: For extra color, heat 1 tablespoon oil in a skillet over medium-high. Sear chicken 1–2 minutes per side until lightly browned. Transfer to the baking dish.

Bake: Place chicken in the prepared dish and bake for 18–25 minutes, depending on thickness, until the internal temperature reaches 165°F (74°C) in the thickest part.

Rest and serve: Let the chicken rest for 5 minutes so the juices settle. Remove toothpicks before serving. Spoon any pan juices over the top.