Start by preparing the mayonnaise. Put the egg yolk in a bowl and add the mustard, salt and pepper to taste, and vinegar. Beat with a whisk until blended. Add the oil while whisking continuously. Add in scallion and ketchup. Cover and refrigerate until serving time.
Cut the salmon into 4 equal pieces. Set up a work station. Put flour in small dish or bowl; beat egg in a small dish or bowl; place bread crumbs in a small dish or bowl.
Dredge salmon in flour, dip in egg, then coat with bread crumbs. Repeat with other salmon pieces.
Heat oil to a medium high temperature. Cook the salmon pieces 2 to 3 minutes. Do not overcook, or fish will be dry. Drain on paper towels.
Serve with lettuce greens, scallion mayonnaise, lemon wedges, and pickled ginger.