Pierce the spaghetti squash all over with a fork. Cook on HIGH in the microwave until the squash is starting to soften when pressed, about 15 minutes, turning halfway through cooking.

Let the spaghetti squash cool for about 10 minutes, then cut in half lengthwise. Scoop out and discard the seeds. Using a fork, scrape out the strands and transfer to a bowl or cutting board. Set aside.

Heat a large nonstick skillet over medium-high heat. Add the chicken, season with ¼ teaspoon salt and ¼ teaspoon ground pepper, and cook until no longer pink in the center. Transfer to a bowl and set aside.

Decrease the heat to medium and heat the olive oil in the skillet. Add the onion and cook, stirring occasionally, until the onion is tender, 4 to 5 minutes.

Stir in the garlic, oregano and red chili flakes, and cook for 1 minute.

Add the crushed tomatoes, along with the remaining ¼ teaspoon salt and pepper. Bring to a boil, then reduce heat to a simmer. Cook for 10 minutes.

Preheat the broiler.

Stir the chicken, Kalamata olives and parsley into the tomato sauce, just until combined. Add the spaghetti squash and toss with tongs until combined. Spread evenly in the skillet.

Top the squash with feta cheese, then place the skillet under the broiler until the cheese is starting to melt, 1 to 2 minutes. Serve.