Preheat your oven to 350°F. Lightly grease a 9x13 glass baking dish with nonstick spray.
Mix the filling: In a large mixing bowl, combine the cooked chicken, cream of chicken soup, and milk. Stir until smooth. Add in the frozen vegetables, cheddar, and mozzarella cheese. Mix well and spread evenly in the baking dish.
Prepare the biscuits: Cut each biscuit into quarters. Dip each piece into the melted butter to coat completely.
Top the casserole:
For faster cooking, arrange the biscuit pieces in a single layer, close together but not stacked.
For a thicker biscuit top, you can layer slightly, but be aware that it will take longer to bake through.
Bake uncovered:
Single layer: Bake for 30 to 35 minutes, or until the biscuits are golden and cooked through.
Layered or double biscuit topping: Bake for 45 to 50 minutes. Check for doneness by gently lifting a biscuit piece from the center to ensure it’s fully cooked.
Let rest for 5 to 10 minutes before serving. The filling will thicken as it sits.
Notes
I used jumbo buttermilk biscuits (not flaky layers). If you use smaller-sized biscuits, you may need more than 2 tubes — just watch the total ounces and adjust as needed to cover the top.
Using a glass baking dish 350°F works well. If using metal, you can stick with 350°F or go slightly higher (375°F) depending on your oven.
Don’t thaw the vegetables. Keeping them frozen helps prevent excess moisture.