Roast the spaghetti squash according to these instructions
Add the olive oil to a medium-sized saute pan and heat to medium-high. Add the onion and saute, stirring occasionally, until transluscent, about 5 minutes.
Add the mushrooms, broccoli, and garlic. Continue cooking, stirring occasionally, until mushrooms and broccoli have softened, about 10 to 15 minutes.
Add baby spinach, cover, cook until wilted, 2 minutes.
Once spaghetti squash has finished roasting, use a fork to scrape out the "noodles." Serve spaghetti squash with desired amount of sauteed vegetables, marinara sauce, and fresh grated parmesan cheese on top (or skip the parm to make this vegan and paleo).