Heat oven to 425°F and line a rimmed baking sheet.
Prep carrots and parsnips into even 1/2-inch sticks for uniform cooking.
Toss vegetables with olive oil, salt, and pepper on the sheet.
Roast for 20 minutes, then flip and roast 10–15 minutes until tender and browned.
Melt butter in a small saucepan. Stir in maple syrup, thyme, and cinnamon.
Simmer glaze 2–3 minutes, stirring, until glossy and slightly thickened.
Transfer hot vegetables to a bowl. Pour over glaze and add vinegar.
Toss to coat, then return to the sheet for 3–5 minutes to set the shine.
Finish with parsley. Taste and adjust salt and pepper before serving.