Preheat and prep: Heat your oven to 400°F (200°C). Line a baking sheet with parchment or lightly oil a baking dish. Pat the chicken breasts dry with paper towels.

Make the filling: Warm 1 tablespoon olive oil in a skillet over medium heat. Add the onion and cook until softened, about 3–4 minutes. Stir in the garlic and cook 30 seconds until fragrant. Add spinach and cook until wilted (or warmed through if using thawed spinach). Squeeze out excess moisture, then transfer to a bowl.

Stir in cheeses and seasoning: Add feta, cream cheese (if using), lemon zest, a pinch of red pepper flakes, and 1/4 teaspoon each of salt and pepper. Mix until combined. The filling should be thick and not watery.

Butterfly the chicken: Place a hand flat on a chicken breast and, using a sharp knife, slice horizontally to create a pocket without cutting all the way through. Repeat with remaining chicken.

Season the chicken: In a small bowl, mix 1 teaspoon paprika, 1 teaspoon oregano, 1 teaspoon salt, and 1/2 teaspoon black pepper. Rub 1–2 tablespoons olive oil over the chicken, then sprinkle the spice mix on both sides.

Stuff and secure: Spoon the spinach-feta mixture evenly into each pocket. Don’t overfill. Secure the open edges with toothpicks or tie with kitchen twine to keep the filling in place.

Sear for color: Heat a large oven-safe skillet over medium-high heat with a little olive oil. Sear the stuffed chicken 2–3 minutes per side until golden. Work in batches if needed. Transfer to the baking sheet or keep in the oven-safe skillet.

Bake until done: Bake for 12–18 minutes, depending on thickness, until the internal temperature reaches 165°F (74°C). If you didn’t sear, add a couple of minutes.

Rest and serve: Let the chicken rest 5 minutes. Remove toothpicks. Squeeze fresh lemon over the top and serve with your favorite sides.