Preheat your oven to 400°F (200°C). Line a sheet pan with parchment for easy cleanup.
Trim the fennel bulbs, remove the tough core, and slice them into thin wedges. Arrange the fennel slices evenly across the prepared sheet pan.
Segment the oranges and grapefruit, catching any juice in a small bowl. Distribute the citrus segments over the fennel on the pan, then drizzle with a little citrus juice for extra flavor.
Scatter the thinly sliced ginger slices over the vegetables and citrus. The ginger will release fragrant oils as it roasts.
In a small bowl, whisk together olive oil, honey or maple syrup, salt, and pepper. Pour this mixture evenly over the fennel, citrus, and ginger, then toss gently to coat everything well.
Place the sheet pan in the oven and roast for about 20 minutes, or until the fennel is golden and caramelized around the edges, and the citrus is slightly softened.
Remove the pan from the oven and give everything a gentle toss. The vegetables should be tender, with some charred spots, and fragrant from the ginger and citrus.
Serve the roasted fennel and citrus immediately, garnished with extra fresh citrus segments if desired. Enjoy the bright, caramelized flavors and crunchy-tender textures.