Bring a large pot of salted water to a boil over medium-high. Add pasta, and cook until al dente, about 10 minutes. Drain and set aside.

Meanwhile, heat 1 tablespoon oil in a large cast-iron skillet over medium-high. Add corn and ½ cup jalapeños; cook, stirring occasionally, until corn is well charred, 10 to 12 minutes. Transfer to a plate, and set aside. Wipe skillet clean.

Heat remaining 1 tablespoon oil in skillet over medium-high. Add panko, ⅓ cup red onion, ½ teaspoon salt, ¼ teaspoon black pepper, and remaining ¼ cup jalapeños. Cook, stirring often, until panko is evenly browned and onions are softened, 2 to 3 minutes. Reduce heat to low, and stir in ¾ cup mozzarella until melted. Cook, stirring to break panko mixture into small, crispy clusters, about 3 minutes. Remove from heat. Set aside.

Melt butter in a large pot over medium. Add remaining ⅓ cup red onion; cook, stirring occasionally, until softened, about 2 minutes. Add flour; cook, whisking constantly, 1 minute. Whisk in milk, and bring to a boil. Boil, whisking constantly, until mixture thickens into a creamy sauce, 2 to 3 minutes. Gradually fold in remaining 2 cups mozzarella until melted. Remove from heat; stir in mayonnaise, sugar, remaining 2 teaspoons salt, and remaining ¼ teaspoon black pepper.

Fold pasta and 2 cups corn mixture into sauce. Season with additional salt to taste. Top with panko mixture and remaining corn mixture.