In a wide deep skillet or saucepan, add chicken and enough water to cover. Bring to a boil, cover with lid and reduce heat to medium-low. Simmer until chicken is cooked through, about 15 to 20 minutes. Drain and let cool.
Meanwhile, in a blender or food processor, blend tofu, cream cheese, 1/2 cup cheddar, hot sauce and milk until smooth; stop to scrape down sides of bowl as needed. Add parsley, onion powder, dill, garlic powder and cayenne (if using) and blend to combine.
Preheat oven to 350°F. With 2 forks, finely shred chicken in an 8-inch square baking dish. Pour cheese mixture over top. Add blue cheese and mix well. Sprinkle with remaining 1/4 cup cheddar and bake until bubbly, 20 to 25 minutes. Sprinkle with scallions and serve with whole-grain chips or sliced vegetables.