Preheat oven to 350°F. Spread the pecans out on a baking sheet and drizzle with maple syrup; stir around with a spoon to coat them well. Sprinkle with salt and pepper and bake for 5 minutes; stir and bake them for another 5 minutes, until the syrup is thick and glaze-like. Remove from the oven and spread the nuts on a piece of foil or a plate to cool.
In a large pot of boiling salted water, cook the Brussels sprouts for 5 minutes; drain and run under cool water. Shake off any excess water and run the sprouts through a food processor with a 1/8"-1/4" slicing disk, or patiently cut them all thinly by hand. Transfer to a large bowl.
In a bowl or jar, shake or whisk together all the dressing ingredients. Toss the Brussels sprouts with as much dressing as you like; let marinate for about an hour.
Right before serving, add the pecans.