Bring a large pot of salted water to a boil. Cook the pasta according to the package directions until it's al dente. Drain and rinse under cold water until cooled.
Add the cooked pasta, lettuce, Mexicorn, tomatoes, olives, cheddar cheese, and green onions in a large bowl.
In a small bowl, mix the mayo, sour cream, taco seasoning, Rotel tomatoes with the juices from the can, and chopped cilantro until combined.
Pour the dressing over the salad and gently mix until evenly coated.
Cover the bowl with plastic wrap and refrigerate for 1 hour to allow flavors to blend. Uncover and serve.