Combine breadcrumbs, mustard seeds, salt, pepper, sesame seeds, thyme and lemon zest in a bowl and set aside.
Heat butter in pan until almost melted, then tip in combined ingredients.
Sauté until ingredients are light brown and your breadcrumb mixture has a light crunch to it, then remove from heat and set aside to cool.
Place mustard and mayo in a bowl and mix together.
Place salmon fillets on baking tray, skin side down, and spread mustard and mayo mixture on the top.
Once breadcrumb mixture has cooled, add egg and combine.
Spoon breadcrumb mixture on top of salmon fillets pressing down a little to ensure it adheres to the mustard and mayo.
Place salmon into a preheated oven at 350 and cook for approx. 15 minutes, dependent upon desired temperature.