Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper for easy cleanup.
Use a vegetable knife to thinly slice the fennel bulb into delicate, even strips. Spread the fennel slices across the baking sheet.
Zest the oranges and grapefruit, then sprinkle their zest evenly over the fennel and set aside for now.
Grate the fresh ginger over the salmon fillets, ensuring each piece gets a good covering of the fragrant root.
Juice both oranges to obtain about ¼ cup of citrus juice, then drizzle it over the salmon and fennel on the sheet.
Drizzle the olive oil over the salmon, fennel, and citrus, then season with salt and black pepper to taste.
Arrange the salmon fillets on top of the fennel slices on the sheet, skin-side down if applicable, leaving space between each piece.
Place the sheet in the oven and bake for about 12–15 minutes, until the salmon edges are crispy and the flesh is opaque and flaky.
Once cooked, remove the sheet from the oven and sprinkle the citrus zest over the salmon and fennel for a fresh, fragrant finish.
Transfer the salmon to plates, spoon some of the roasted fennel and citrus slices alongside, and serve while warm.
