Cut a lengthwise slit down center of tenderloin to within 1/2 inches of bottom. Open tenderloin so lays flat, then on each half make another lengthwise slit down the center to within 1/2 inches of bottom. Cover with plastic wrap.
Flatten to 1/4 inch thickness, remove wrap, sprinkle with 1/4 teaspoons each celery salt, garlic powder and pepper, then layer with cheese, spinach and ham. Press down gently.
Roll up jelly-roll style, starting with a long side. Tie the roast at 1 1/2 in to 2 inches intervals with kitchen string. Sprinkle with remaining seasonings and place 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 Transfer to serving platter, and allow to stand for 10 minutes before removing strings and slicing.