Pre-heat oven to 375 degrees and line a baking sheet with foil.
Place squash halves on baking sheet. Put ½ Tbsp butter in each acorn squash half and sprinkle with ½ tsp salt and ½ tsp pepper. Roast squash for about 45 minutes, until it's tender to the fork.
While the squash is roasting, prepare the quinoa. Bring quinoa and vegetable stock or water to a boil in a medium saucepan. Once boiling, lower to a simmer, cover, and let cook for about 15 minutes, until all water is absorbed. Fluff with a fork and set aside.
Add olive oil to a large skillet over medium heat. Add onions, mushrooms, garlic, and habanero pepper and sauté while occasionally stirring for about 7 minutes, until beginning to brown. Sprinkle about ¼ tsp salt and ¼ tsp pepper into mixture and squeeze lemon juice over.
Turn heat to low and add the cooked quinoa to the veggie mixture. Add in spinach and stir to combine and wilt spinach a bit. Stir in feta cheese and parsley.
Spoon quinoa mixture into acorn squash halves and top with additional feta and parsley. Add dried cranberries, if desired.