Preheat your oven to 350°F (175°C).
In a mixing bowl, combine the softened cream cheese and butter until well blended. Add the milk and mix until smooth.
Stir in the shredded chicken, diced green onions, diced bell pepper, salt, and pepper. Mix well to ensure all the ingredients are evenly incorporated.
On a cutting board, unroll one tube of croissant dough. Pinch together the cut lines to form four rectangles from the eight croissants.
Place 1/4 cup of the cream cheese and chicken mixture in the center of each rectangle. Bring the corners together and pinch them closed.
In a separate bowl, whisk the egg (optional) and brush it over each croissant for a golden finish.
Bake in the preheated oven for 13-15 minutes or until the croissants turn a beautiful golden brown.
Remove from the oven and let them cool slightly before serving. Enjoy the delectable cream cheese chicken croissants!