1. Preheat oven to 375°F (190°C).

2. In a large skillet over medium heat, melt butter and sauté onion and garlic until translucent.

3. Add cooked chicken and mixed vegetables to the skillet and stir to combine.

4. Pour in cream of chicken soup and milk, whisking until smooth.

5. Season with salt, pepper, and Italian seasoning, then simmer for 5 minutes.

6. Grease a 9×13-inch baking dish and spread the chicken mixture evenly in the dish.

7. Arrange biscuit dough pieces on top of the filling, spacing as desired.

8. If using, whisk egg and water and brush over biscuits for a golden crust.

9. Bake uncovered for 25–30 minutes or until biscuits are golden and filling is bubbling.

10. Let rest for 5–10 minutes before serving.