Preheat your oven to 375°F (190°C). Prepare your baking sheet with parchment paper.

Cut the spaghetti squash in half lengthwise and remove the seeds. Brush with olive oil and season with salt and pepper before placing cut-side down on the baking sheet.

Cut the chicken breast into pieces, season with salt and pepper, and place on the baking sheet. Bake for about 45 minutes.

Melt butter in a skillet over medium-low heat. Sauté diced onions until softened, then add garlic and cook until fragrant.

Once baked, scrape the spaghetti squash into strands and dice the chicken. Mix these with the sautéed onions, Greek yogurt, cheese, salt, and pepper.

Spoon the mixture into the spaghetti squash shells, top with remaining cheese, and broil for 3-5 minutes.

Remove from the oven, let cool slightly, and serve.