Roast the acorn squash:
Preheat your oven to 400°F (200°C).
Prepare the acorn squash by cutting off the top and bottom to create a flat base. Carefully slice the squash in half, and scoop out the seeds and stringy flesh.
Place the squash halves cut-side up on a baking sheet. Drizzle with olive oil and rub it into the squash. Season with salt and pepper.
Turn the squash halves over, cut-side down, and roast for 30 minutes in the preheated oven.
Make the sausage filling:
While the squash is roasting, heat 1 tablespoon of olive oil in a large skillet over medium-high heat.
Add the diced onion and cook for about 2 minutes until softened and slightly charred.
Add the crumbled sausage, minced garlic, and Italian seasoning, and cook for 5 minutes, stirring occasionally, until the sausage is fully cooked.
Add the fresh spinach and cook for another 5 minutes until it wilts.
Stir in the dried cranberries and chopped pecans, mixing everything together. Adjust seasoning with salt and pepper if necessary.
Stuff the acorn squash:
After 30 minutes, remove the squash from the oven and flip them cut-side up.
Evenly divide the sausage mixture among the four squash halves, filling them generously.
Reduce the oven temperature to 350°F (175°C) and bake the stuffed squash for an additional 10-20 minutes until the filling is heated through.