Optional: coat the baking dish with ½ Tablespoon of sesame oil for a more savory, Korean taste.
Cook the sushi rice as per normal. (Click through for detailed instructions.) I soak mine before cooking in a rice cooker, with a piece of dried kelp for a more savory flavor. 15-20 minutes before the rice is done, preheat the oven to 425F/ 218C/ 198C fan.
5-10 minutes before the rice is done cooking (takes about 40 minutes in a rice cooker), take the salmon out of the fridge. (We don't want to cook it fridge cold or the texture won't be great. But not more than 15 minutes for food safety's sake!) Cut into 1 by 1.5 inch pieces, then mix well with the mayonnaise, cream cheese, soy sauce, vinegar/ pickle brine, sesame oil and sugar. Put aside.
Once the rice has cooked, mix the rice with the seasoned sushi vinegar (the vinegar combined with sugar and salt) by cutting and folding, not stirring.
Spread the seasoned rice on the casserole dish till it's completely filled.
Add ½ of the Furikake evenly and liberally all over rice, followed by the salmon.
Bake in a pre-heated oven at 425F/ 218C/ 198C fan for about 12 minutes or till the salmon is cooked through but still flaky. (The cooking time will change depending on hot your oven runs or how big you cut the pieces.)
Add the rest of the furikake- if you're using the fish roe, you may not need all the remaining furikake, so taste before you season.
Whilst the dish is in the oven, cut the avocado and other toppings. Keep them in the fridge till you need them. Once the hot casserole is out of the oven, top with the avocado slices, spring onions, sesame seeds, sliced chilies etc. Enjoy!