Preheat the oven to 425°F.

Combine crushed garlic, lemon juice, mustard, olive oil, and pepper in a small bowl; mix well.

Carefully cut a lengthwise slit down the center of the tenderloin to within 0.5 inch of the bottom (do not cut all the way through).

Open the tenderloin so it lies flat. On each half, make another lengthwise slit down the center to within 0.5 inch of the bottom. Cover with plastic wrap and flatten to 0.25-inch thickness with a meat mallet.

Remove the plastic wrap. Spread half of the garlic/Dijon mixture on the inside of the pork. Layer the cheese, spinach, sun-dried tomatoes, and prosciutto on top, pressing down gently.

Roll up the pork jelly-roll style, starting with a long side. Tie the roast at 1.5-inch to 2-inch intervals with kitchen string.

Season lightly with salt and the remaining garlic/Dijon mixture. Place the tenderloin on a rack in a shallow baking pan.

Bake, uncovered, at 425°F for 25-30 minutes or until a meat thermometer reads 160°F. For a browned top, place under the broiler for 5 minutes, then transfer to a serving platter or cutting board.

Let stand for 10 minutes before removing the string and slicing. Slice into 8 pieces.