Make the marinade: In a microwave-safe container, combine the dashi, rice vinegar, soy sauce, sugar, and mirin. Microwave at 1,200 watts for 1–2 minutes. Stir well until the sugar is completely dissolved, then transfer the marinade to a shallow dish. A dish with a lid is ideal for marinating.
Prepare the vegetables: Thinly slice the carrot, onion, and mini bell peppers.
Prepare the salmon: Cut the salmon into pieces about 2 inches in size. Season with salt and pepper, then coat evenly with potato starch or cornstarch. A small fine-mesh strainer makes it easy to dust the starch evenly over the salmon.
Cook the vegetables: Heat 1 tablespoon of vegetable oil in a frying pan over medium heat. Add the vegetables and sauté until they become tender. Transfer the vegetables to the marinade.
Pan-fry the salmon: Add 4 tablespoon of vegetable oil to the same pan and heat over medium heat. Add the salmon and pan-fry for about 3 minutes on each side, or until lightly golden brown and cooked through. Drain the excess oil well, then transfer the salmon to the marinade while it is still warm.The salmon can be enjoyed right away, or refrigerated and marinated for 2–3 hours for even more flavor.