So I could use some suggestions. I have a staple dish I make when I don't want to spend much time fussing in the kitchen:
If you want really easy, get a bag of frozen veggies (peas, corn, carrots, nothing large) and just dump some in before you mix it all up. Minced garlic could also work if you're baking it that long.
Less easy but still easy, slice up some onion. Won't add too much flavor (unless its red, but even then), but the texture change could be nice. Could also do much the same with some chopped up bacon (because bacon makes everything better).
Bonus points if you saute it first (with the chicken maybe, as @Dreikin suggested) though that does increase the time needed to prep and the number of dishes used.
Super lazy move: BBQ sauce after it's done.