Preheat the oven to 375 degrees F (190 degrees C). Place 1 rack in center position and another 4 inches from broiler. Spray a rimmed sheet pan with cooking spray.

Toss together cabbage and apples with 3 tablespoons oil, 1/2 teaspoon salt, and 1/4 teaspoon pepper on prepared sheet pan and arrange in an even layer.

Pat pork dry and season with remaining teaspoon salt and 1/4 teaspoon pepper. Whisk together remaining 2 tablespoons oil with mustard, vinegar, honey, and thyme in a small bowl. Spread over all sides of pork and set pork on top of cabbage and apples.

Roast on center rack until an instant-read thermometer inserted into center of thickest part of each tenderloin registers 130 degrees F, about 25 minutes.

Remove pan from oven and turn oven to broil. When broiler is hot, put pan on top rack and broil until pork has a golden-brown crust, thermometer registers 145 degrees F, and cabbage and apples have a light char, about 5 minutes. Cover pan loosely with foil and let pork rest 10 minutes before slicing.

Serve pork warm with cabbage and apples, garnished with parsley.