Preheat oven to 180°C (350°F).
In a bowl, mix chicken, mayonnaise, sour cream, heavy cream, beef bouillon, salt, pepper, and sage.
Stir in caramelized onions and green beans.
Spread the mixture into a greased baking dish.
Bake in the oven for 25-30 minutes.
Top with Swiss cheese slices.
Arrange biscuit quarters over the cheese layer.
Spray biscuits lightly with cooking spray.
Bake again for 8 to 10 minutes, until the biscuits are golden brown and the casserole is bubbly.
Serve hot and enjoy your French Onion Chicken Casserole!