Heat oven to 350 degrees. Coat a 9x13-inch baking dish with nonstick spray.
In a large pot, bring 4 quarts water and 1 tablespoon salt to boil. Add pasta, stirring well, and return to boil. Cook until al dente, about 8-10 minutes, and drain.
In a large skillet or Dutch oven, sauté beef and onion over medium heat until browned, about 5 minutes. Drain well. Stir in garlic and taco seasoning until fragrant, about 30 seconds.
Add corn, tomatoes, beans, tomato sauce, green chilies, salt, and pepper. Bring to boil. Reduce heat; simmer 5 minutes.
Stir in cream cheese, 1 cup cheddar cheese, and 1 cup pepper jack. Simmer until cheese is melted. Add pasta, stirring until evenly coated. Season to taste with salt and pepper.
Pour into baking dish; top with remaining cheddar and pepper jack. Bake until golden brown and cheeses are melted, about 20 to 25 minutes. Let stand for 5 minutes before serving.
Top with sour cream and scallions, if desired.