Preheat the oven to 400°F / 200°C / Gas Mark 6, no fan (if you have a convection/fan oven, reduce the temperature by about 20° or follow the manufacturer's instructions).
Season the salmon with salt and pepper on both sides.
Place it in the smallest baking dish that it can fit into.
In a medium bowl, whisk all the ingredients for the marinade (orange juice, zest, maple syrup, oil, mustard, garlic). Season lightly with salt and pepper.
Pour the marinade over salmon. You can leave the fish to marinate for 30 minutes or bake it straight away.
Bake for about 14-20 minutes depending on the thickness of the fillets and can vary depending on the oven (the fillets shown on the photos needed 20 minutes). To check if the fish is cooked through, measure its internal temperature in the thickest part of the fillet, it should be 145°F (63°C). You can take the fish out of the oven when the thermometer registers 140°F (60°C) - the fish should come to the safe temperature while resting.
Leave the fish to rest for 5 minutes - pour it with the sauce while it's resting.
Serve and enjoy!