Preheat oven to 400°F (200°C).
Prepare the squash: Cut acorn squash in half and remove the seeds. Brush with olive oil and season with salt and pepper.
Roast: Place squash halves cut-side down on a baking sheet. Roast for 30–40 minutes, until tender.
Cook the filling: Heat olive oil in a skillet over medium heat. Add onion and garlic; cook until fragrant.
Add sausage and vegetables: Stir in sausage and cook until browned. Add diced bell pepper; cook 3–4 minutes.
Combine everything: Add cooked quinoa or rice, thyme, sage, and cinnamon. Stir well, then fold in cranberries and nuts. Season with salt and pepper.
Stuff the squash: Flip roasted squash halves and fill with the sausage mixture. Sprinkle with cheese if desired.
Bake again: Return to the oven for 10 minutes to warm through and melt cheese.
Serve hot: Garnish with herbs or extra nuts and enjoy!