Cut the salmon into bite-sized pieces.
Thinly slice onion, cheongyang pepper, and green onion.
Mix soy sauce, water, mirin, sugar, minced garlic, and pepper to make the marinade.
Place the prepared salmon and vegetables in a container.
Pour the marinade over and refrigerate for 4-6 hours to let it marinate.
Serve the soy-marinated salmon and vegetables on a plate.