I was skeptical of spaghetti squash at first. We grew them in our garden mostly for the landowner, but have had such a harvest I've simply had to come to terms with them. I had always been displeased with them in the past, I think because I was expecting them to be...well, squash. Or to be pasta. Truth is, they are not quite either of those foods but once I learned to stop expecting them to be something they are not, things have worked out well.
And so I offer you a convert's guide to spaghetti squash, the vegetable-based pseudo-noodle that serves as an excellent vehicle for pesto and other pasta sauces.
For me, the key to getting nicely noodley spaghetti squash has been to bake and fluff them with a little bit of oil or butter, to help the strands separate. So, start off with your oblong squash, cut it in half lengthwise and scoop out the seeds so you have two long oval bowls. Drop a dab of butter or a splash of olive oil into each half, put them on a baking dish or tray, and pop them in the oven at 350. Bake for about 40 minutes. Baking them face-down can preserve a bit more moisture, which helps separate the strands. I usually forget this fact until after baking, but it still works out
When the inside flesh seems soft (i.e., easy to stick a fork into), pull them out of the oven and prepare for the magical step that turns a baked squash into a bowl of pseudo-noodles. Drop a big spoonful of pesto into the squash cavity and spread it around. Then, simply take a fork and gently rake along the cavity of the squash, pulling the strands gently away from the edges, and fluffing them up. The pesto will start to mix in without much effort.
You should be accumulating a nice pile of fluffed up "noodles" in your squash at this point; continue the process till you've pulled all the flesh away from the rind. Then, stir in additional pesto till you reach your desired level of sauciness.
Now, you should have a nice little self-contained squash rind noodle bowl. You could eat it right now if you want, but if you have a little more patience it will get even better. Take those noodle bowls, top with cheese, and stick them back in the oven. Keep an eye on them, as this stage is short: 10 minutes or less. Once the cheese is melted and bubbling slightly on the top, pull them out and serve.
If you get some smaller squashes, they make great self-contained individual-sized bowls; a family or other group of picky eaters could even customize the type or amount of sauce, cheese, or other toppings, so everyone gets their preferred style. This is also a great way to enjoy traditionally pasta-associated sauces for people avoiding grains.
We have also done these twice-baked squash with tomato based sauces, or with butter and cheese for an almost mac-and-cheese version. All are delicious.