Start by preheating your oven to 375°F (190°C). In a large bowl, mix the shredded chicken, cream of chicken soup, and thawed vegetables. Add half the shredded cheese and season with salt and pepper. This forms the creamy, veggie-packed base of your casserole.
Once the filling is ready, pour it into a greased 9x13 inch baking dish. Spread it evenly so every bite gets a balance of chicken and veggies. This step is key to ensuring it bakes evenly and looks delicious when served.
Now, in a separate bowl, combine the milk, Bisquick mix, sour cream, melted butter, and minced garlic. Stir until the mixture is smooth. This will create a light, fluffy layer that bakes beautifully over the filling.
Pour the biscuit batter over the chicken mixture in the dish. Spread it gently with a spatula to cover everything. Sprinkle the remaining cheese on top for that golden, bubbly finish. Bake for 30-35 minutes until the top is golden and the sides are bubbling with creamy goodness.
Let the casserole sit for about 5–10 minutes before serving. This helps the layers set and makes it easier to scoop out those perfect servings.