Preheat grill to 350º to 400º (medium-high) heat. Remove silver skin from tenderloin, leaving a thin layer of fat.
Sprinkle pork with 1 tsp. salt and 1/2 tsp. pepper. Combine mustard and next 4 ingredients. Rub mustard mixture on pork; cover and let stand 10 minutes.
Preheat oven to 450º. Cut squash and zucchini into 1/2-inch slices; cut into half moons. Toss with 1 tsp. olive oil and remaining 1 tsp. salt and 1/4 tsp. pepper. Place on an aluminum foil-lined jelly-roll pan, and bake 20 minutes or until tender.
Meanwhile, grill pork, covered with grill lid, 10 to 12 minutes on each side or until a meat thermometer inserted into thickest portion registers 155°. Remove from grill; cover with foil, and let stand 10 minutes. Slice pork, and serve with squash medley. Sprinkle with thyme.
Loved the pork tenderloin! I would definitely make this again. I used dried thyme in place of fresh. I coated the tenderloin with the marinade and left it in the refrigerator overnight. It was great. Like the previous reviewer, I think this would be good on other meats - chicken or lamb. I did not try the squash part of the recipe either, but served it with squash casserole and butterbeans.