We've made this two ways-starting with a box mix, Suddenly Salad Classic, or with bagged tri-color pasta and our own dressing.
Simply boil the pasta according to directions, drain and rinse with cool water, and drain again. We like ours with an Italian type vinegrette (you can control the calories if you choose your own dressing). Our favorite toppings to mix in are mozzarella chunks (in a pinch I'll cut up string cheese), pepperoni (the minis work great, but since our daughter cannot have nitrates/nitrites the brand we buy we have to cut up), and black olives. We've made it with cut up chicken as well.
It is a hearty lunch or makes a great side dish. It has always been a crowd pleaser and is super simple.