Preheat oven to 425°F and line large baking sheet with aluminum foil.
Cut acorn squash in half widthwise and scoop out seeds. Cut a small piece off each end to form a base.
Brush acorn squash with 1 tsp olive oil and salt. Place face down on baking sheet.
Roast for 20-30 minutes. Back of squash should feel soft. Remove from oven and set aside.
(omit if vegetarian) Heat one iron skillet over med/hi heat. Add bacon and stir to brown. Remove and drain on paper towel.
In same skillet, heat 1½ tbsp olive oil over low heat and add all the sliced onions, stirring to coat. Sprinkle with ½ tsp salt and cook stirring every 5 minutes for a total of 20 minutes. Once onions are a golden brown, remove and set aside.
In a separate iron skillet add remaining olive oil and heat over medium. Add mushrooms stir & cook for ~1 minute. Add garlic and stir, cook for another ~1 minute.
Add ground beef (or meat substitute) with 3/4 tsp salt, pepper and poultry seasoning, and cook until brown.
Lower heat and stir in spinach to wilt. Remove from heat and add in the caramelized onions. Stir in the cooked bacon (omit if vegetarian).
Preheat your broiler. Stuff all roasted squash halves and place the baking sheet under broiler. Broil until the top is crisp, ~4 minutes.