Preheat oven to 400 degrees. Halve the spaghetti squash lengthwise, then remove seeds. Place cut side-down on a lightly oiled baking sheet and roast for 35 minutes, until tender.

While the squash roasts, halve peel, and thinly slice the red onion. Thinly slice the scallions, keeping whites and greens separate. Mince or grate the garlic.

Heat 1 tablespoon olive oil in a medium pan over medium heat. Add the onion and cook, tossing, 6-7 minutes, until slightly caramelized. Season with salt and pepper. Add the garlic and scallion whites to the pan and cook another 1 minute, until fragrant. Set aside in a medium bowl.

In the same pan, heat another 1 tablespoon olive oil over medium heat. Add the Portobello steaks and cook 4-5 minutes per side, until very soft. Season with salt and pepper. Thinly slice and set aside.

Wipe out the pan with a paper towel. Add the walnuts over low heat and cook, tossing, until toasted and fragrant, 2-3 minutes. Set aside in the bowl with the onions.

When the spaghetti squash is finished cooking and cool enough to handle, scrape out flesh with a fork into the bowl with the onions and walnuts. Toss in the Parmesan cheese until thoroughly combined, then season generously with salt and pepper.

Serve the spaghetti squash topped with the sliced Portobello steaks and sprinkled with goat cheese and scallion greens. Enjoy!