Preheat grill on high heat. Add corn and poblano pepper and char on all sides, about 10 minutes for the corn and 5 minutes for the poblano pepper. Alternatively, you can broil the corn on the cob and poblano pepper on high, carefully rotating both every few minutes, until both are charred all over.
Allow corn and poblano to cool, then cut the corn off the cob and remove the skin and seeds from the poblano pepper. Finely dice the poblano pepper.
In a liquid measuring cup or small mixing bowl, combine the mayonnaise, sour cream (or Mexican crema), cilantro, lime juice and zest, chili powder, cayenne pepper, salt and black pepper. Use a whisk to mix the dressing.
Cook pasta in salted water according to package instructions. Strain water and pour pasta into a serving bowl.
To the pasta, add charred corn, poblano pepper, red onion, cotija cheese and dressing. Toss so everything is evenly coated in the dressing.