Preheat the oven to 400 degrees.
Cut the tops off the acorn squash so you have a stable base, then halve them lengthwise and scoop out the seeds.
Drizzle with olive oil and salt and pepper. Place skin side up on a parchment lined baking sheet and bake for 35 minutes, until squash is tender.
While the squash is roasting, remove the sausage (pork, turkey or vegan) from the casing and brown it, until cooked through. Set aside on a paper towel.
In the same skillet, saute the onions and parsnips in 1 tbsp. of olive oil with some salt and pepper over medium heat, until the onions are translucent, about 8 minutes. Add the apples and cook for another 5 minutes. Add the sausage back into the skillet and combine.
Remove from the sheet pan while warm, but cool enough to handle, and transfer to a baking dish deep enough to hold the squash boats.
Fill the squash halves with the sausage and apple mixture.
Return to the oven for 20 minutes at 350 until everything is warmed through.
While the squash is in the oven, make the topping. In a bowl, mix the crushed pretzels, parsley and lemon zest in a bowl.
Remove the stuffed acorn squash from the oven and place on a serving platter. Top with the crunchy pretzel topping.