If you're only feeding 4-6 people, I suggest cooking the spaghetti squash whole, then only using half of the squash when you're ready to saute with the tomatoes. I like my spaghetti squash not too hard, not too soft. It shouldn't be mushy, you should be able to still separate the strands of squash. Plus, in this recipe, you'll saute the spaghetti squash for a few minutes, and it will soften in the pan.
Using a sharp paring knife, carefully pierce (I really mean stab) the spaghetti squash in a few places (about 6 slashes is good). Place squash on plate. Microwave on high for 10-15 minutes, turning/rotating the squash halfway during cooking.
I had a 3 1/4 pound spaghetti squash. 12 minutes total was perfect.
The squash is done with a fork very easily pierces through the squash, if there is resistance - microwave for an additional 1-2 minutes.
Carefully (the squash will be steaming hot!), use a chef's knife to cut the squash in half, lengthwise. The squash should be soft and easy to cut. Remove and discard the seeds. Use two forks to scrape apart the strands of the squash. For this recipe, we'll only use half of the spaghetti squash, about 4 cups.
Heat a large saute pan over medium heat with the olive oil. Add in the garlic and cook for 1 minute. Add in the tomatoes and basil and cook for another minute. Turn heat to medium-high and add in the spaghetti squash and toss. Season with salt and pepper and drizzle in the balsamic vinegar. Taste the squash - adjust seasoning. If the squash still needs a bit more time to cook through, cover and cook for 2 minutes. If the squash texture is perfect, toss in the grated cheese and serve immediately.