With a mandoline or a sharp knife cut carrots into short 1/8-inch thick julienne strips. With a sharp knife cut bell pepper into short 1/8-inch thick julienne strips. In a steamer set over simmering water steam carrots, covered, 5 to 6 minutes, or until crisp-tender, and transfer to a bowl. Steam bell pepper 1 to 2 minutes, or until crisp-tender, and add carrots.
Halve fennel bulb lengthwise and core. Cut fennel into short 1/8-inch thick julienne strips. Halve onion lengthwise and cut into short 1/8 inch thick julienne strips. Add fennel and onion to carrot mixture. In a saucepan bring remaining ingredients to a boil, stirring to dissolve sugar, and pour over vegetables. Marinate vegetables covered and chilled, at least 1 hour and up to 1 week. Serve relish chilled or at room temperature with poultry, veal, pork, or lamb.