Preheat the oven to 425°F. Combine the maple syrup, sambal oelek, orange zest, and orange juice in a shallow dish. Add the salmon fillets, turn to coat, and set aside.

Toss the brussels sprouts and shallots with the olive oil, spread in a single layer on a rimmed baking sheet, and season with 1/2 teaspoon salt and 1/4 teaspoon pepper. Roast until the sprouts are browned and crispy in spots, 12 to 15 minutes, tossing once halfway through cooking.

Toss the sprouts again, push a few sprouts to the side, and place the fillets on the baking sheet. Pour the salmon marinade over the fish, season with salt and pepper, and roast until the salmon is opaque throughout and the sprouts are tender and crisp, 10 to 12 minutes, depending on the thickness of the fillets. Divide between 4 dinner plates and serve.