Preheat oven to 400 degrees Fahrenheit and line a baking sheet with a silicone baking mat, parchment paper, or foil.
In a small bowl, whisk together olive oil, rice vinegar, ground cinnamon, salt, and ground black pepper until combined.
Pour mixture onto chicken, onion, fresh cranberries, and acorn squash and toss to coat.
Evenly spread coated chicken, onion, cranberries, and acorn squash onto prepared baking sheet. Roast in oven for 20-30 minutes, or until chicken breasts reach an internal temperature of at least 165 degrees Fahrenheit and acorn squash can be easily pierced with a fork.
Notes
If you can't find a sweet onion, try using a mild yellow onion.
You use frozen cranberries instead of fresh, if desired.