Preheat the oven to 400°F and position a rack in the middle. Prepare the squash by cutting it in half lengthwise from stem to bottom and scooping out the seeds and pulp from the cavity.
Place the squash halves cut side down on a baking sheet and roast for 40 to 45 minutes until the cut edge caramelizes and the flesh is fork-tender. Note: Cooking time may vary depending on the squash's weight and oven differences.
While the squash roasts, prepare the ground beef filling. Heat olive oil in a skillet over medium heat, then add diced yellow onion and sliced celery. Season with salt and cook for 5-7 minutes until onion turns golden. Add minced garlic and cook until fragrant.
Add sausage and cook until completely browned.
Incorporate diced apple and cook for 5 minutes until softened and liquid reduces.
Add raisins, brown sugar, ground cinnamon, and Worcestershire sauce. Mix well and turn off the heat.
Once the squash is done, scoop out some flesh to create space for the filling and mix it with the ground beef mixture. To check if the squash is cooked, insert a fork or knife into the flesh; if it goes in easily, it's done. Stuff the roasted squash halves with the sausage filling.
If needed, heat the stuffed squash in the oven for an extra 10 minutes before serving to ensure thorough heating.
