I did this for lunch on Wednesday, and it was super easy and really tasty.
All you need is some olive oil, a small onion, pasta, and some jarred salsa.
First, start a pot of water going for the pasta. Then, dice the onion. When the water boils, toss the pasta in.
In a skillet, heat some olive oil and saute the onion, until it gets a little browned, but still firm. Pour salsa in with the onions, and stir. Let that cook a little more. When the pasta's done, drain it and toss it in with the salsa and stir to coat it. Enjoy!
I made about 1/4 pound of penne pasta, and used about 2/3 cup of medium tostitos salsa. Feel free to use whatever brand you prefer.
The sauce came out tasting sweet, spicy, and a little smoky. It didn't really taste like salsa anymore, and if I hadn't made it myself, I probably wouldn't have known it was made from salsa.