01 - Bring a large pot of salted water to a rolling boil. Add the fusilli or rotini and cook according to package directions until al dente. Drain thoroughly and rinse under cold running water to halt cooking. Set aside to cool completely.
02 - Preheat a grill or grill pan to high heat. Place the corn directly on the grate and grill for 8 to 10 minutes, turning every couple of minutes, until kernels are lightly charred and blistered. Let cool, then stand each ear upright and slice the kernels from the cob. If using frozen corn, sauté in a dry skillet over high heat until golden and slightly charred.
03 - In a large salad bowl, combine the mayonnaise, sour cream, lime zest, lime juice, chili powder, smoked paprika, cayenne pepper (if desired), sea salt, and black pepper. Whisk until smooth and fully blended.
04 - Add the cooled pasta, grilled corn kernels, diced red bell pepper, red onion, green onions, and chopped cilantro to the dressing. Toss vigorously until every component is evenly coated.
05 - Gently fold in the crumbled cotija cheese along with the jalapeño and avocado, if using, taking care not to mash the avocado.
06 - Cover and refrigerate for at least 30 minutes so the flavors meld. Taste before serving and adjust salt, pepper, or lime juice as needed.