Slit and butterfly fish fillets to form a large flat area.
Mix breadcrumbs, spring onion, lemon rind, lemon juice, mushrooms and egg yolk or 1/2 egg substitute together.
Place 1/4 of stuffing on one end of each fillet. Roll up fillets, dip in beatened egg white or rest of egg substitute then coat with dried breadcrumbs.
Heat oil in a heavy based fry pan. Fry fish until flaky, about 5 minutes each side.