Heat oven to 375.
Lightly rub olive oil on the inside of the acorn squash before placing face down on a baking sheet (you can line it with parchment to make clean up easier).
Place Squash in the oven for about 30 minutes or until soft to the touch.
Mix brussel sprouts and cauliflower in a bowl, drizzle with olive oil and sprinkle with salt and pepper.
Put veggie mix on another baking sheet and place in the same oven, watching (brussel sprouts are tender and you don't want them to over cook), about 25-30 minutes.
When they start getting crispy looking, they are done.
While they are in the oven, use a small skillet and sauté the garlic until you can smell it (about 3 minutes) and then add sliced mushrooms stirring frequently so they don't burn, for about 15 minutes or until the start turning golden brown.
Once it is all out of the oven, assemble on the plate.
Put your acorn squash in the center, and add the mushrooms to the middle.
Next place roasted veggie around the squash, then the peppers, and lastly the sprouts.