Whisk together the oil, maple syrup, Worcestershire, vinegar, salt, pepper, garlic powder and onion powder in a shallow baking dish. Add the carrots and toss to coat. Cover with aluminum foil and refrigerate, turning occasionally, for at least 4 hours and up to overnight.
Preheat the oven to 350 degrees F and preheat a grill to medium-high.
Transfer the foil-covered baking dish to the oven and bake until the carrots are fork-tender, 20 to 25 minutes. Grill the carrots until grill marks appear, a few minutes per side. Serve on the buns with mustard, coleslaw and crispy fried onions.