At the beginning of the recipe it says preheat to 325. At the end of the recipe it says to cook in a preheated 425 oven? What to do?

It sounds like the 325 is for the pot of rice, onions, and broccoli stems. Then cool the rice and prepare the broccoli florets and chicken. Then when combined, preheat the oven for the finished dish.

I'm going to go out on a limb and guess that one of them is a misprint, probably the 325, since you are basically just using the oven to brown the dish which would result better at 425 degrees.