If you're doing the whole keto/low carb thing, there is no better substitute for pasta than Palmini. Made from hearts of palm, these yummy "noodles" will take on just about any flavor you throw at them without giving a flavor of their own. They are a bit pricey, but the bright side is you just have to open a can, drain them and dump them into the sauce. If you opt to use palmini, you're not going to have any pasta water to help you thicken up the sauce. You can either opt to simmer the sauce down to a thicker consistency, or take the shortcut of adding a slurry of about 1/4-1/2 teaspoon of cornstarch or arrowroot powder with a tablespoon of water to the sauce and cooking for an extra minute or two to thicken.