For Pan-Frying:

1. In a medium-sized bowl, whisk together soy sauce, kewpie mayo, dijon mustard, black pepper, and salt until smooth and well combined.
2. Dice the salmon fillets into two-inch cubes. Place the diced salmon into the bowl of marinade, using a spoon to thoroughly coat each cube in the sauce.
3. Allow the salmon to marinate for at least 15 minutes, or up to 30 minutes, for better flavor absorption.
4. Heat a large non-stick skillet over medium heat. Add a bit of oil or butter to coat the pan. Once the pan is hot, add the salmon cubes, skin-side down if applicable.
5. Cook for about 4-5 minutes on each side, or until the salmon is golden brown and cooked through. If you prefer a slightly crispier texture, you can cook the salmon a bit longer. Serve immediately with the glaze from the marinade.

For Baking:

1. Preheat the oven to 400°F (200°C). Prep a baking sheet with a coating of oil or butter.
2. In a small bowl, whisk together soy sauce, kewpie mayo, dijon mustard, black pepper, and salt until smooth and well combined.
3. Dice the salmon fillets into two-inch cubes. Place the diced salmon into the bowl of marinade, using a spoon to thoroughly coat each cube in the sauce.
4. Allow the salmon to marinate for at least 15 minutes, or up to 30 minutes, for better flavor absorption.
5. Bake the salmon on the prepped baking sheet in the preheated oven for 9-10 minutes, or until the salmon flakes easily with a fork.
6. After baking, switch to the broiler setting and broil for an additional 2 minutes to get a slightly caramelized, crispy top. Remove from the oven, garnish if desired, and serve!