1.Make salsa verde: place parsley, dill, garlic, lemon juice, capers and mustard into the base of food processor and process to a chunky paste. Add mayonnaise and process to just combine. Season with salt and refrigerate until required.
2.Season fish fillets with salt and pepper. Dip 1 fillet in egg and coat well in panko crumbs. Place on lined baking tray and repeat with remaining fillets.
3.Heat oil in 2 frying pans over medium- high heat. Cook fish for 2 mins on each side until golden and just cooked through. Drain on paper towel.
4.Place rocket leaves and slices of avocado on base of each bread roll. Dollop salsa verde mayo on each lid. Place 3 pieces of flathead on top and cover with lid. Serve.