In a large mixing bowl, combine the shredded chicken, mashed avocado, cream cheese, Greek yogurt, lime juice, garlic powder, and cayenne pepper (if using). Mix until everything is well combined. Season with salt and pepper to taste.
Preheat your broiler on high.
Lay the slices of bread on a baking sheet and lightly butter one side or drizzle with olive oil.
Spoon generous amounts of the chicken and avocado mixture onto the unbuttered side of each slice of bread. Top each with a sprinkle of shredded cheddar cheese.
Place the baking sheet under the broiler for about 5-7 minutes, or until the cheese is bubbly and golden brown. Keep a close eye to prevent burning!
Once done, remove from the oven and let cool for a minute. If desired, garnish with fresh cilantro or parsley for added freshness and color.
Notes
Feel free to adjust the spice level by adding more or less cayenne pepper.