To CookAdd vegetarian oyster sauce, sesame oil, brown sugar, water, white pepper, ginger and garlic into a bowl and mix together until fully combined. Heat over medium-low heat, stirring to avoid burning. Take off heat when sauce is reduced by half. Set aside to cool.Preheat oven to 180°C. On a lined baking tray, coat sauce over tofu on both sides and bake for 20 mins. Flip and bake for another 20 mins.Add sushi seasoning into rice, mix and let sit for 15 mins. To shape sushi buns, spoon 2-3 tbsp of sushi rice into an egg ring and press to mold into shape. Place sushi buns on heated pan to sear the surface. Assemble the burger by adding avocado, spring onions, wasabi, pickled ginger, cucumber and desired amount of sauce before topping off black sesame seeds on top of sushi bun.