Combine sriracha and sour cream. Set aside.
Combine all Tartar sauce ingredients and set aside.
Combine salad ingredients. Do not add lemon and salt yet.
Sprinkle fish fillets with salt. Beat eggs and milk together. Combine flour, salt, pepper and garlic powder.
Dip each fillet forst into the flour mixture, shake off excess, then coast with egg-milk mixture. Dip back again into flour mixture, coating well and shaking off excess.
Fry fish fillets in oil until crispy brown on bother sides, approx 3 - 4 minutes in total.
Toast inside of each brioche bun.
Build the burgers: Divide Sriracha sauce in two and spread on each bottom brioche bun. Squeeze a little lemon and salt over salad and mix together quickly. Layer salad ontop of sriracha sauce. Next add the fish fillet, followed by tartar sauce and finish with the brioche bun top.