In a large bowl, season the fish pieces with some sea salt and pepper. Cover and allow to refrigerate for 15 minutes, or until ready to cook.
Place your coconut milk in a blender together with the gluten-free flour and blend until completely smooth. Set aside.
In a large skillet or Dutch oven over medium-high heat add your oil and heat until hot. Add onion, bell peppers, mushrooms, ginger, and garlic.
Sprinkle with a pinch of sea salt and cook until vegetables soften, about 5 minutes.
Add the curry paste, curry powder, and vinegar; cook whisking constantly until the vinegar is evaporated/cooked off, about 1-2 minutes.
Stir in your coconut milk mixture then reduce the heat to a low and bring to a gentle simmer.
Carefully nestle the seasoned fish pieces to your simmering sauce.
Cook, stirring occasionally until fish is cooked through and flakes easily with a fork,6-8 minutes depending on the fish you’re using.
Divide your hot curry equally into 4 serving bowls, and garnish with cilantro leaves and green onions.
Serve with cooked brown rice if desired and enjoy!