For Chicken Marinade: Whisk together soy sauce, oil, ginger, garlic and black pepper in a medium shallow baking dish. Add the chicken breast and turn to coat. Cover and marinate in the refrigerator for at least 4 hours. Heat a large grill pan over high heat until smoking. Remove chicken from marinade and season with salt to taste. Grill for 4 to 5 minutes on each side until just cooked through. Let rest 5 minutes, slice each breast on the bias into 6 slices.
For the Red Curry Peanut Sauce: Heat peanut oil in a medium saucepan over high heat. Add the curry paste and saute for 3 to 4 minutes. Add the soy sauce, coconut milk and lime juice and bring to a simmer. Whisk in the peanut butter and cook for 5 minutes. Season with salt and pepper to taste.
For the Peanut Relish: Combine all ingredients in a small bowl and season with salt and pepper.
To Assemble: Preheat oven to 375 degrees F. Lay tortillas out on a flat surface. Divide both of the cheeses among the tortillas. Top the cheese with 3 slices of the chicken, some of the red onion and cilantro. Fold the tortillas over to form a half moon and brush the tops with peanut oil. Place on a lightly oiled baking sheet and bake for 5 to 7 minutes, until the cheese melts. Serve 2 on a plate, drizzle with the red curry-peanut sauce and sprinkle with peanut relish and cilantro.