Add the TVP slices to a large bowl or plate and cover with boiling water. Let it sit for about 20 minutes, or until the TVP is tender. You can soak the TVP slices overnight in the refrigerator as well.
Drain the TVP slices and squeeze them to remove as much water as possible. Transfer to a food processor and add the vegan nuoc mam, sugar, onion powder, ground black pepper, dried dill, garlic, vinegar, dulse flakes and mushroom seasoning if using.
Process for 15-30 seconds, or until it forms a flaky paste (a bit like flaked tuna). Add the cornstarch and process a few more seconds. You want the mixture to hold together when you squeeze it between your hands, but it should still be slightly crumbly.
Cut your nori sheet in two rectangles of about 5x2.5-inch. Press down half of the mixture onto each nori sheet into a 1/2-inch thickness. Press it down firmly.
Heat 2 tablespoons of oil in a non-stick skillet. Once hot, use a spatula to transfer your fish fillets to the skillet, with the nori sheet facing down. Shallow-fry for 3-4 minutes, or until the nori sheet is crispy. Flip the fillets and cook for another 3-4 minutes on the other side.
Serve immediately with your favorite sauce on top of steamed rice and/or with sautéed vegetables on the side. For extra flavor, I recommend cooking your fish fillets a couple of minutes in your sauce.