Preheat your oven to 425°F (220°C). Line a baking sheet with parchment paper.
Carefully cut the acorn squash in half lengthwise. Scoop out and discard the seeds and stringy parts. Brush the cut flesh of the squash with 1 tablespoon of olive oil and season with salt and pepper.
Place the squash halves cut-side down on the prepared baking sheet. Bake for 20-25 minutes, or until the flesh is easily pierced with a fork.
While the squash bakes, heat the remaining 1 tablespoon of olive oil in a large skillet over medium-high heat. Add the ground sausage and cook, breaking it apart with a spoon, until browned and cooked through. The internal temperature should reach 160°F (71°C). Drain any excess fat.
Add the minced garlic and sliced green onions to the skillet. Cook for 1 minute more until fragrant. If using spinach, add it now and stir until just wilted.
Remove the skillet from the heat. Stir in the cooked wild rice, 1/2 teaspoon salt, and 1/4 teaspoon black pepper. Mix to combine.
When the squash is tender, remove it from the oven. Carefully flip the halves so they are cut-side up. Use a spoon to gently scoop out some of the cooked flesh to create a larger cavity if desired.
Spoon the sausage and rice mixture evenly into the squash halves.
Return the stuffed squash to the oven and bake for 5-7 minutes more, until the filling is heated through. Serve immediately.