You could try mixing some (tbs or two) cornflour with a little water to make a paste, stir that through some thickened cream (250/300ml?), mix in some dried or fresh herbs of choice then stir that together with your chicken and veg mixture till it just starts to thicken. I would also add a good amount of fresh pepper and some cheese, otherwise it is going to be very bland indeed. Bake as directed in recipe.
If you want the garlic flavour you should fry it at the same time as the chicken, or maybe use garlic powder or garlic infused oil. Incidentally, if it is simplicity you are after you could further amend this dish to use a pre-cooked chicken or leftovers and forego the saucepans altogether.