Roasting endive and fennel calms the vegetables' slightly bitter flavor. Along with sweet blood oranges and dried figs, they combine well with the peppery arugula in this salad; mustard vinaigrette is tossed in.
Preheat oven to 400 degrees. Toss fennel, endives, rosemary, 2 tablespoons oil, 1 teaspoon salt, and 1/4 teaspoon pepper in a large bowl. Spread mixture in a single layer on a rimmed baking sheet. Roast, tossing occasionally, until fennel and endives are well browned, about 35 minutes. Discard rosemary.
Transfer fennel mixture to a large serving bowl. Add vinegar, mustard, remaining tablespoon oil, the figs, and orange segments. Toss well to combine. Let cool to room temperature.
Just before serving, toss fennel mixture with the arugula. Season with salt and pepper, if desired.