Preheat oven to 425 F. Line a rimmed sheet pan with parchment for easy cleanup.
Toss brussels sprouts with olive oil, salt, and pepper. Spread cut side down on the pan.
Roast until just starting to brown, about 15 minutes.
Whisk maple syrup, balsamic, Dijon, garlic, and red pepper flakes in a small bowl.
Add pecans and half the maple-balsamic mixture to the pan. Toss and roast 6–8 minutes, until sprouts are tender and edges are deeply browned.
Finish with remaining glaze and thyme. Toss to coat, taste, and adjust seasoning. Serve warm.