Preheat the oven to 375ºF.
To prepare the fennel:Cut off the stalks where they attach to the bulb; reserve some of the fronds. Trim off 1/8-inch to 1/4-inch from the root base. Cut the remaining bulb into eight wedges; don't core (see below). To make the citrus dressing:Whisk the following ingredients together in a medium-sized bowl: 1/3 cup of the reserved mandarin orange juice, olive oil, Dion mustard, tarragon, red pepper flakes, sea salt, and pepper.
Add the fennel wedges to the bowl and toss. Marinate for about 20 minutes; toss often.
Arrange fennel wedges single layer on a parchment lined baking sheet. Roast for about 45 minutes or until tender and golden.
In the meantime, warm up a small, dry cast iron skillet over medium-low heat. The idea is to warm up the skillet, but don’t overheat. When the skillet is warm, increase the heat to medium-high and add the pine nuts. Toast, while stirring and shaking, for about a minute, or until they begin to give off a nutty aroma and turn a bit golden.
Arrange the fennel and mandarin orange segments on a bed of arugula. Sprinkle with the pomegranate seeds and pine nuts. Drizzle with any remaining citrus dressing. Garnish with chopped fennel fronds.