Preheat oven to 375 degrees.
Lightly rub 1 teaspoon olive oil on flesh side and sprinkle with salt and black pepper. Place squash flesh-side down on a parchment or foil lined baking sheet pan. Bake until tender, about 30 - 45 minutes.Remove from oven; flip squash flesh-side up and set aside. Keep warm.
In a large skillet over medium heat, heat remaining oil.
Add sausage to pan and break into small pieces; cook until browned, about 5-7 minutes.
Add spinach and garlic, mix. Wilt spinach, remove from heat.
Mix in walnuts, Parmesan cheese.
Divide mixture evenly into the centers of squash halves.