In a large pot of boiling water, parboil the Brussels sprouts for 5–7 minutes.
Drain and set aside.
Cut the acorn squash in half cross-wise, scoop out seeds.
Cut each squash ring in half and place in a large bowl.
Add 1 tablespoon of olive oil and toss.
Place on a sheet pan, sprinkle with chile powder, season with some salt and roast for 10 minutes.
Place the onions and Brussels sprouts in the bowl and toss with the remaining olive oil. Sprinkle with salt and pepper.
Place on the sheet pan with the squash and roast for 10 minutes until the sprouts are tender. Shut the heat off and keep the veggies in the warm oven until your ready to serve.
Notes
I usually leave the skin on the squash, however, depending on how fresh the squash is, the skin can be very tough. The skin can be removed before or after roasting if desired.