Cook the pasta according to package directions in salted water. Drain the pasta then run cold water over it to stop the cooking process.
Place the chopped red onion in a bowl and cover with cold water. Soak for 10 minutes, then drain. This makes them less pungent.
In a large measuring cup, whisk together the mayo, sour cream, jalapeno, lime juice, cilantro, chives, garlic powder, and chili powder. Splash milk into the mixture until it is pourable. Taste and season with additional salt and pepper, as needed
Toss the pasta with the dressing, vegetables, and cheese. Refrigerate at least an hour, preferably several hours. Serve cold.