Preheat oven to 350 degrees F.
Cut the butter in chunks and place in the bottom of a 9 x 13-inch baking pan. Place in oven to melt butter; remove when butter is melted.
In a large bowl, mix the milk and baking mix; set aside.
Dissolve the stock cubes in the liquid chicken stock. Place the soup in a bowl and gradually mix in the stock mixture to keep the mixture smooth. Set aside.
Assemble casserole as follows and DO NOT MIX OR STIR INGREDIENTS:
Distribute shredded chicken over melted butter evenly
Distribute veggies over the chicken evenly
Distribute the onion over the veggies evenly
Distribute the cheese over the onion evenly
Pour baking mix batter over the top evenly
Pour the soup/stock mixture over the top evenly
Place in preheated oven and bake for 45-50 minutes, or until top is beginning to brown.
Remove from oven and let stand 10 minutes before serving.