Preheat your oven to 375°F (190°C).

In a medium bowl, combine the chopped spinach, feta cheese, sun-dried tomatoes, garlic powder, onion powder, oregano, salt, and pepper. Mix well to create the filling.

Place each chicken breast between two sheets of plastic wrap or parchment paper. Gently pound the chicken with a meat mallet or rolling pin until about 1/2 inch thick.

Lay each flattened chicken breast on a clean surface and evenly distribute the filling mixture over each piece, leaving a small border around the edges.

Roll up each chicken breast tightly, starting from one end, and secure with toothpicks or tie with kitchen twine.

In a large oven-safe skillet, heat the olive oil over medium-high heat. Add the chicken rolls and sear for about 3-4 minutes on each side until golden brown.

Drizzle with balsamic vinegar if using, then transfer the skillet to the preheated oven. Bake for 20-25 minutes or until the chicken is cooked through (internal temperature should reach 165°F).

Remove from the oven and let rest for 5 minutes before removing the toothpicks or twine. Slice and serve warm.