Preheat the oven to 400 degrees F. If the carrots are thick, cut them in half lengthwise; if not, leave whole. Slice the carrots diagonally in 1 1/2-inch-thick slices. (The carrots will shrink while cooking so make the slices big.) Toss them in a bowl with the olive oil, salt, and pepper. Transfer to a sheet pan in 1 layer and roast in the oven for 20 minutes, until browned and tender. Toss the carrots with minced dill or parsley, season to taste, and serve.