Place all the ingredients for the sauce in a saucepan and heat gently on low-medium heat, stirring occasionally.

Once the sugar has completely dissolved, let it come to a boil and simmer for about 5 minutes. If you prefer a thicker sauce, simmer for a longer time.

Let it cool to room temperature. Store in an air tight jar/container.

Mix ½ cup of the teriyaki sauce with the flank steak. Let it marinade for about an hour. (Alternatively, you can add the 1/2 cup of the Teriyaki sauce ingredients mixed well together, without cooking)

Brush a non stick frying pan with some peanut oil generously and heat till the oil starts to shimmer.

Grill the steak strips in batches (do not over-crowd the pan), 30 seconds on each side (longer depending on how thick the slices are). If any steak or marinade juices accumulate in the pan, remove this before adding another batch, as the meat will not caramelize properly with moisture in the pan.

Let the steak rest for about 5-10 minutes.

If there is leftover uncooked marinade, this can be added to the hot (clean) pan, to be reduced slightly to be used as a glaze for the Rice Buns.

Place all the ingredients in a small saucepan and heat on medium heat. Stir to make sure the sugar and salt dissolve. Once it comes to a light boil, remove from the heat and set aside.

Let the washed rice dry in a colander or sieve for about 10 minutes. Place the rice and the water in a rice cooker and let it cook according to the manufacturer’s instructions. Keep the rice warm.

Please note that sushi rice is best eaten on the day it is cooked. It can dry out and taste extremely stale. Therefore, cook the rice and keep it warm until ready to be mixed in with the seasoning.

When you're ready to make the sushi burgers, spread the rice in a larger bowl or container (bamboo container is better, but I used a glass container). Sprinkle ¼ cup of black sesame seeds on top. Keep a wet cloth handy.

Measure out roughly 1/3 of a cup of the sushi seasoning and sprinkle on top of the rice, and using a wide spoon (like a rice paddle) “chop” and fold the rice lightly, taking care not to squash or break the rice.

Roughly divide the rice into 6 equal portions.

Shaping Buns by hand - Using wet hands shape each portion into a burger bun. Keep them on a plate covered with the wet cloth.

Shaping Buns with an Egg ring - Place wet egg rings on a parchment paper and place a portion of rice in the egg ring. Using a wet spoon, press the rice into the egg rings until it forms a compact, molded rice "bun".

In a small non stick frying pan, brush some oil and sear just one side of each rice bun for about 5 minutes on medium heat, or until it starts to caramelize a little. Set aside and keep covered with a wet cloth.

Mix the Mayonnaise and wasabi together until mixed thouroughly. Cover and keep it in the fridge till needed.

On the bottom sushi burger bun, brush some Teriyaki glaze/teriyaki sauce. Place some teriyaki steak strips on top and place the egg on top of the steak, followed by lettuce and/or Nori. Brush the top Sushi burger "bun" with some teriyaki sauce and spread some Wasabi Mayonnaise. Place this ontop of the lettuce. Top the Sushi burger with Nori Furikake and Pickled Ginger.

Other optional fillings - teriyaki chicken, avocado, grilled mushroom, cucumber.

Wrap with foil or parchment paper until ready to eat.