Begin by boiling a large pot of salted water over high heat. Once boiling, add the rotini pasta and cook according to package instructions until al dente, typically about 9-11 minutes. Drain the pasta and rinse it under cold water to stop the cooking.

If using fresh sweet corn, preheat your grill to medium-high heat. Grill the corn for about 10 minutes, turning occasionally, until lightly charred. Once grilled, let it cool and carefully cut off the kernels. If using frozen corn, simply thaw it in warm water, drain, and set aside.

In a large mixing bowl, combine the mayonnaise and sour cream with freshly squeezed lime juice. Whisk in the chili powder, salt, and pepper until smooth and creamy.

Add the cooled rotini pasta to the mixing bowl along with the sweet corn kernels. Toss in the crumbled cotija cheese, chopped cilantro, and sliced green onions. Gently fold the ingredients together until everything is evenly coated with the creamy dressing.

Taste and adjust seasoning as needed, then cover the bowl with plastic wrap and chill in the refrigerator for at least 30 minutes.

After chilling, give the salad one final toss. Serve in a large bowl or platter and garnish with additional cotija cheese, cilantro, and a sprinkle of chili powder.