1. Make the tartar sauce: Stir together all ingredients and set aside.
2. Make the fish: Rinse fish and pat dry. Season liberally with salt. In a shallow dish, combine flour, dill, parsley, onion powder, hot paprika, garlic powder, and white pepper. In a separate shallow dish, make an egg wash by whisking together milk and eggs. Pour panko in a separate dish. In a wide, heavy bottomed pan, heat oil to 350 degrees. Dredge trout in seasoned flour, dip in egg wash, and coat with panko. Gently lay trout fillets in oil, being careful not to crowd the pan. Once fillets are golden on one side, about 4 minutes, carefully turn over and brown other side. Set on a wire rack or paper towels to drain.
3. Toss romaine with tomato, radish, and green onion, then season with salt and pepper. Toast the baguette and, once it’s cool enough to handle, split it. Tuck fish fillets inside baguette, then top with tomato mixture and tartar sauce.