Heat the oven to 400 degrees F.
Whisk rice vinegar, soy sauce, ginger, honey and oil together in a bowl.
Add the chili pepper and the mushrooms, stir around a few times to coat everything, then let the mix sit for 10 minutes.
Spread the mushrooms out on a baking sheet and roast until tender (about 10 minutes).
Sprinkle with green onion slices and serve.