Preheat oven to 425°F (220°C).

Cut a lengthwise slit down the center of the pork tenderloin, stopping 1/2 inch from the bottom.

Open the tenderloin so it lays flat.

On each half, make another lengthwise slit down the center to within 1/2 inch of the bottom.

Cover the tenderloin with plastic wrap and flatten it to 1/4 inch thickness.

Remove the plastic wrap.

Sprinkle with 1/4 teaspoon of celery salt, 1/4 teaspoon of garlic powder, and 1/4 teaspoon of pepper.

Layer the tenderloin with provolone cheese, fresh spinach, and deli ham.

Press down gently on the filling.

Roll up the tenderloin jelly-roll style, starting with a long side.

Tie the roast at 1 1/2 to 2-inch intervals with kitchen string.

Sprinkle with the remaining celery salt, garlic powder, and pepper.

Place the tenderloin on a rack in a shallow baking pan.

Bake uncovered for 25-30 minutes, or until a meat thermometer reads 160°F (71°C).

Transfer the tenderloin to a serving platter.

Let it stand for 10 minutes before removing the strings and slicing.

Serve warm.