You will need the following ingredients: cooked chicken, pasta, tomatoes, red onions or scallions, olives, cheese, and salad dressing. I'll get to the specifics and quantities in a moment, and there are also a couple of variations of how you can make this.
The easiest way to get cooked chicken is to go to the grocery store and buy one of those rotisserie chickens. If you already have leftovers in your fridge that's perfect. Last time I made this I didn't have any leftovers, so I pulled a couple of frozen boneless chicken breasts out of the freezer and cooked them first, which adds some time but allows you flexibility in preparing the chicken the way you like it. You should end up with at least two cups of cut-up chicken, maybe even three.
For pasta I like to use fusilli (the ones that look like corkscrews) or farfalle (bowties), but you can use whatever kind you like. Let me just point out, though, that bigger ones like ziti don't make sense to use in this recipe. And no spaghetti, smartass. Don't bother with anything fancy; as long as you cook it properly (which is to say, al dente) it will taste fine. I like to use Barilla boxed pasta. Cook the whole box, but use only about 2/3 of it for this. Set aside the rest and use it for something else (tough to go wrong with olive oil, garlic, and cheese). Don't cook only 2/3 of the box, because you know you'll eventually end up with a bunch of orphan boxes cluttering up your cupboard or pantry.
Grape tomatoes cut in half work nicely, but you can use the vine kind or whatever, maybe you're even growing tomatoes in your yard. I like the grape ones because that pint container is just the right size for this. (It's true that Virgos like precision, but this isn't anything that calls for a lot of careful measuring, so I just wing it.) Likewise, one can of olives, split into halves, is fine. You don't need as much onion as you think, so get a couple of smallish ones and just dice them up. I like to use feta cheese in this, but some people don't like it. That's a great thing about cheese: there are so many different kinds. If your cheese isn't already conveniently broken into small chunks (like feta is), you'll want to do some approximation of that. (Optional: something like celery or cucumbers, for a little variation in texture and additional nutritional value. Just dice them up like the other stuff.)
Is the pasta done yet? I hope you were paying attention and didn't overcook it. Drain it and put it back in the pot or a really big bowl, and start throwing in all the other stuff. After you add each item, add a little bit more dressing and stir well. This helps everything get coated nicely. I recommend an oil-based dressing like Italian, Caesar, or Greek, because they are flavorful, coat well, and aren't too heavy. You wouldn't want to use a creamy dressing, that would just be too heavy, blech. Paul Newman's dressings are great, I almost always use one of those.
That's pretty much it. If possible, prepare it ahead of time and refrigerate before eating. You may find that, like chili, this tastes better after a night in the refrigerator. One other variation I do once in a while is to use salami instead of chicken. Ask at your deli if they will cut you a hunk of Genoa salami and not slice it. Take it home and dice it up. Five or six ounces of salami is probably plenty, and if your deli clerks know what they're doing they will know how much to cut. I kind of prefer scallions when I make this with salami, but you can take it in whatever direction you feel like. Obviously, if you're a