Put the shio koji and yuzu pepper paste into a clean plastic bag and mix well. Add the salmon fillets. Coat the fish with the marinade well. Chill in the fridge overnight.
Make vertical slices into the peppers and remove the seeds. Remove the stems from the shitake mushrooms and score their caps for decoration.
Grease a frying pan lightly with oil and place the fish and vegetables. The sides of the fish and vegetables facing up on the pan will be the sides facing down when plated. Cook over medium heat and cover with a lid for 8 to 10 minutes.
After it's 80% cooked through, flip over and continue to cook for a further 2 to 3 minutes without the lid on. When the insides of the mushroom cups have started to release their moisture, it is time to plate. You don't need to turn them over.
You don't have to prepare any vegetables to garnish but shiitake mushrooms absorb the salmon umami taste quite well and are delicious.
I used the cooking method shown in Recipe ID: 967046 and made just adjustments. The vegetables don't entirely absorb the umami of the salmon when cooked on a grill because all the fat will just drip off.
If you prepare this fish in the method shown (on a frying pan), it'll turn out fluffier and softer than when cooked on a grill.
Story Behind this Recipe
I like fish marinated Saikyo-style, so I thought it would be a good idea to marinate some in shio koji. Just add a little yuzu kosho to give the fish a fresh fragrance. My family loves this, so I make this dish quite often.
By using a plastic bag, you'll be able to make the salmon absorb the marinade very well while your hands stay clean. When you fry the fish and vegetables, have the sides you want showing on the plate down on the frying pan. This way, you'll avoid having charred bits showing when you plate and serve your fish and veggies. Try to cook everything in the same pan so flavors of the fish and shio-koji settle into the vegetables.