Preheat oven to 400°F.  Line a baking sheet with aluminum foil, then mist with cooking spray.  Set aside.

Using a sharp knife, very carefully cut the spaghetti squash in half lengthwise.  (I find it helps to microwave the squash for 2-3 minutes before cutting to soften it up.)  Use a spoon to scoop out and discard the seeds and stringy pulp in the center of the squash.  Then brush the flesh of the squash evenly with olive oil, sprinkle with salt and pepper, and place the squash halves cut-side-down on the prepared baking sheet.

Bake for 30-35 minutes, or until the inside of the squash is cooked through and shreds easily with a fork.  (Larger squash halves will take longer to bake.)  Remove from oven, and let the squash cool for a few minutes.

Using a fork, shred the inside of the squash until all of the flesh is spaghetti-like.  Then add 1/2 cup (more or less) pizza sauce and 1/4 cup shredded cheese to each squash half, and gently give it a toss until all of the spaghetti-ed squash is evenly coated with the sauce.

Sprinkle a few pizza evenly toppings on top of the sauce on each squash half, followed by about 1/4 cup mozzarella cheese, followed by a few more pizza toppings as desired.

Turn the oven to broil.  Place the baking sheet with the spaghetti squash pizzas in the oven (I placed mine on a rack 1/3 from the top of the oven) and broil for 4-6 minutes — keeping a close eye on the pizzas so that they do not burn — until the cheese is melted and starts to turn a little bit golden.

Remove from the oven, and serve immediately.