1 Place salmon fillets, skin side down, on prepared baking sheet. 2  Mix remaining oil, thyme, and lemon zest in a small bowl. 3  Spread thyme mixture over salmon fillets, dividing equally. 4  Season with salt and pepper. 5  Let stand 10 minutes to allow flavors to meld. 6  Bake salmon until just opaque in center, 15-18 minutes. Preheat oven to 275°F. Line a rimmed baking sheet with aluminum foil. 2  Brush with 1/2 tablespoon oil. 3  Place salmon fillets, skin side down, on prepared baking sheet. 4  Mix remaining oil, thyme, and lemon zest in a small bowl. 5  Spread thyme mixture over salmon fillets, dividing equally. 6  Season with salt and pepper.