Make sure to pat your fish dry with paper towels before covering it with the mustard sauce. It will still release quite a bit of liquid as it bakes but this way you will reduce the amount of it. Heat coconut oil in a pan over medium heat. Sear the fish for 2 to 3 minutes per side. Season with salt and ground black pepper.
Mix all ingredients for the sauce until everything is well combined. Top the fish fillets with the sauce and serve garnished with fresh basil leaves. Bon appétit!