Marinara type sauces are usually the lowest in fat. A cook can also use ground turkey or vegetarian crumbles to substantially lower the fat content of any pasta dish. I like both ground turkey and the crumbles, and they are a good buy because you don't get nearly as much shrinkage like you do with beef or pork.
Some people really like frozen peas in pasta, but I can't hack that. I like mushrooms, onions and maybe zucchini. Eggplant is also a traditional accompaniment to red sauce, so you don't get much fat with any of those add-ins.
Low fat pasta dishes are easy to do, if you just use a little common sense in the process.