Preheat the oven to 375°F.

In a skillet, heat olive oil over medium heat and sauté garlic for about 1 minute until fragrant.

Stir in chopped spinach and sun-dried tomatoes, cooking until spinach wilts, about 2-3 minutes.

Remove from heat, let cool slightly and mix in feta cheese and oregano.

Place the pork tenderloin on a cutting board and slice it lengthwise to create a pocket.

Stuff the tenderloin with the stuffing mixture, packing it gently.

Secure the opening of the tenderloin with kitchen twine or toothpicks.

Transfer the stuffed tenderloin to a baking dish, season with salt and pepper, and bake for 30-35 minutes until a meat thermometer reads 145°F.

Let the pork rest for 10 minutes before slicing.