Preheat the oven to 220°C (425°F) with a rack in the centre. Line a large rimmed baking sheet with parchment.
Cut the apples into wedges, the squash into 2 cm (3/4 inch) cubes and the onion into wedges. Toss with most of the oil, half the thyme and rosemary and a pinch of salt, and spread on the tray.
Roast the vegetables on their own for 10 minutes while you prepare the pork.
Trim any silver skin from the pork with a thin knife. Rub it with the rest of the oil, herbs, salt and pepper, then brush with the maple syrup mixed with Dijon.
Stir the vegetables, place the pork in the centre of the tray and roast for 18 to 22 minutes, until it reaches 63°C (145°F) in the thickest part. The centre may stay slightly pink; that is safe for whole pork cuts.
Move the pork to a board and rest for 5 minutes (it rises a few degrees as it rests).
Slice into 1.5 cm (1/2 inch) medallions and serve with the roasted apples, squash and onion and any juices from the tray.
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Tips
Pork is safe and juicy at 63°C with a little pink in the centre.
Swaps
Low-FODMAP: leave out the apples and onion; add parsnips instead of apple.