Place the panko breadcrumbs into a bowl and set aside until needed.
Place the fish and potatoes into your Thermomix bowl and mix on speed 5 for 5 seconds to combine. Scrape down the sides of your bowl.
Add the milk, parmesan cheese, garlic, lemon rind, onion flakes, mustard, egg and salt and pepper mix for 6 seconds, speed 5 on REVERSE.
Scrape down the sides of the bowl and mix for a further 5 seconds, speed 4 REVERSE or until combined.
Use a large dessert spoon to scoop up the mixture and shape with your hands to form a ball.
Place the ball into the panko breadcrumbs and gently roll to coat.
Place the coated fish cakes onto a plate and repeat steps 4 and 5 until all of the mixture has been used.
Place the plate of fish cakes into the fridge for 30 minutes to chill, this will help them to hold their shape.
Heat 1 tablespoon of olive oil in a large frying pan over a medium heat and add 4 - 5 fish cakes. The amount of fish cakes you can cook at a time will depend on the size of your frying pan. Cook for 3 minutes before carefully flipping and cooking for a further 2 minutes on the other side or until nice and brown.
Repeat until all of your fish cakes have been cooked.