Preheat and prep: Heat the oven to 425°F (220°C). Line a large sheet pan with parchment or foil for easy cleanup. Pat the pork tenderloin dry with paper towels.

Mix the herb paste: In a small bowl, combine 2 tablespoons olive oil, Dijon, garlic, rosemary, thyme, lemon zest, smoked paprika, 1 teaspoon salt, and 1/2 teaspoon black pepper. Stir into a thick paste.

Season the pork: Rub the herb paste all over the tenderloin, coating evenly. Let it sit while you prep the vegetables to absorb flavor.

Prep the veggies: In a large bowl, toss potatoes, carrots, onion, bell pepper, and Brussels sprouts with 1–2 tablespoons olive oil, 1 teaspoon salt, and 1/2 teaspoon pepper. Add a pinch of red pepper flakes if you like heat.

Arrange on the pan: Spread the vegetables in a single layer on the sheet pan, leaving a space in the center. Place the pork tenderloin in that space so it’s not crowded for better browning.

Roast: Roast for 20–25 minutes, flipping the tenderloin once halfway through. The pork is done when the thickest part reaches 140–145°F on an instant-read thermometer.

Finish with lemon: Squeeze the lemon over the veggies and pork right after you pull the pan from the oven. The acidity brightens everything.

Rest and slice: Transfer the pork to a cutting board and rest for 5–10 minutes. Slice into 1/2-inch medallions. Toss the veggies to coat with any pan juices.

Serve: Arrange slices of pork over the roasted vegetables. Garnish with chopped parsley and a final pinch of flaky salt if you like.