Prep: Preheat the oven to 400 degrees F. Coat a large baking sheet or sheet pan with a little olive oil or line with parchment paper for easy cleanup. Wash and trim the fennel bulbs, leaving only the round bulbs and slicing off the tough bottoms. Slice each bulb into 1-centimeter thick slices. In a small measuring glass, use a fork to whisk together the rest of the oil and mustard.
Dress: Place the sliced fennel into a mixing bowl, add the oil and mustard dressing and use a large spoon to coat all of the surfaces.
Roast: Spread the fennel slices out evenly across the baking sheet, sprinkle salt and pepper over everything to taste, and roast for 35-40 minutes or until golden brown with crisped edges.