Season fish fillets with salt and pepper. Place flour on a plate. Dip fish fillets in flour to coat.
Heat butter and oil in a large frying pan on medium-high. Fry the fish for about 2 minutes each side, until golden brown and cooked through.
Cut Freya’s Brioche Style Buns in half and toast in a frying pan on high heat (or leave them fresh). Spread each half with mayonnaise. Top the bottom halves of the buns with rocket, fish, cucumber and more rocket. Sandwich together with the top halves of the buns and serve immediately.