Heat 1 tbsp olive oil in a large ovenproof skillet over medium heat. Cook the garlic for 30 seconds, then add the spinach and wilt for 2 to 3 minutes. Remove from heat, cool slightly, and mix with the cream cheese, feta, ¼ tsp salt, and the pepper.

Butterfly each chicken breast, season with the remaining salt and extra pepper, then spoon the filling into the center. Fold the chicken closed and secure with toothpicks.

Preheat the oven to 400°F (200°C). Heat the remaining 1 tbsp olive oil in the skillet over medium-high heat and sear the stuffed breasts for 3 to 4 minutes per side until deeply golden.

Transfer the skillet to the oven and bake for 15 to 20 minutes until the chicken reaches an internal temperature of 165°F (74°C). Let it rest for 5 minutes.

Remove the toothpicks, slice the chicken on a diagonal, and serve warm with the pan juices.