I’ve heard people say spaghetti squash is a good substitute for spaghetti, and I think they must be smoking something. It’s delicious with olive oil & garlic, but it’s not fooling anybody.
I’ve discovered a much better approximation of pasta’s texture: Finely julienne rutabagas, and steam them for 20-30 min depending on how soft you like them. Serve the “spaghetti” with meatballs & tomato sauce, other vegetables, under grilled chicken, etc. I like to simmer in broth and maybe spices, then drizzle with olive oil. You could thicken the broth with tapioca/arrowroot to make a sauce. It won’t wrap around your fork, but other than that it’s a pretty good imitation.
Alternative: This works with turnips or probably most root vegetables. Also try frying the “spaghetti” in lard or coconut oil for a different flavor. I think you could also make lasagna noodles, but I have no idea whether you’d cook them first, or how you’d adapt the lasagna recipe.