The best part about making stuffed squash is that it allows you to use up bits and ends in your fridge. You can go in all different directions: try feta and olives; pine nuts and raisins; or chickpeas with turnips and cumin. But the flavor of the squash is truly excellent, so some veggies and sautéed onion is all you really need.
Preheat your oven to 400 degrees.
Heat oil in a large sauté pan and add onion, mushrooms and carrots. Cook until the onions are tender and beginning to brown. Toss rice together with sautéed veggies and fresh herbs, if using. Season with salt and pepper. If you’re using additional ingredients, add them now. Cut the top off the squash, so it makes a nice little top and cut bottom just enough so it can sit flat. Scoop out the seeds and fill the cavity with the rice mixture. Place the top of the squash back on and roast in the oven on a baking sheet until a paring knife easily pierces the flesh, 30 to 40 minutes. Let the squash cool for a few minutes before cutting in half and serving.