Preheat oven to 420 degrees F.
Wash the squash well, dry it and slice it lengthwise.
Scoop the seeds.
Drizzle each squash half with olive oil. Rub it on the inside (the flesh) and on the outside. Use one tablespoon of olive oil per halve.
Season the flesh with salt and pepper.
Arrange it cut side down on a parchment-lined rimmed baking sheet.
Roast in the preheated oven until squash is tender when pierced with a knife or fork, about 45 minutes, to one hour, depending on the size of it.
Remove from oven when done, and let it cool onto the baking sheet for about 10-15 minutes, until able to handle.
Turn it cut side up and using a fork, gently scrape to remove flesh in long strands. Transfer "spaghetti" to a bowl, drizzle with the remaining one tablespoon of olive oil and if desired sprinkle with salt, black pepper, and a squeeze of lemon juice.
Garnish with chopped parsley if desired and pepper flakes for a touch of heat.