Preheat oven to 450F (230C).

Cut the acorn squash lengthwise, removing about one-third in a wedge shape.

Peel the wedge, dice it, and set aside.

Scoop out the seeds from the remaining squash halves.

Cut a thin slice off the bottom of each squash half to level them.

Place squash halves in a microwaveable dish.

Microwave on High for 12 to 15 minutes, or until tender.

Meanwhile, melt canola oil (or butter) in a nonstick skillet over medium heat.

Cook the reserved diced squash, minced onion, and finely chopped celery, stirring occasionally, until softened, about 5 minutes.

Add chopped mushrooms and minced garlic; cook for 2 minutes.

Stir in tomato paste; cook for 1 minute.

In a bowl, combine the onion mixture, fresh bread crumbs, shredded Cheddar cheese (or Jarlsberg), sunflower seeds, salt, and pepper.

Divide the mixture between the squash halves, mounding as needed.

Sprinkle with grated Parmesan cheese.

Bake in the preheated oven for 7 to 10 minutes, or until golden and heated through.