Place chicken breasts in a pot of lightly salted water or broth and bring to a boil.
Simmer for 15–18 minutes, or until chicken is fully cooked.
Remove chicken and shred it using two forks; set aside.
In a large skillet over medium-low heat, combine cream cheese and milk or broth, stirring until smooth and creamy.
Add ranch seasoning mix, black pepper, and garlic powder, mixing well.
Add shredded chicken to the sauce and stir until fully coated.
Stir in cheddar cheese, mozzarella cheese, and crumbled bacon.
Cook for 3–5 minutes, stirring occasionally, until cheese melts and mixture thickens.
Remove from heat and fold in green onions or chives if using.
Lightly butter the cut sides of the sandwich buns.
Toast the buns in a skillet or under a broiler until golden brown.
Assemble sandwiches by spooning generous amounts of crack chicken onto the bottom buns, then top with the bun lids.
Serve warm and enjoy.