Preheat oven to 350 degrees. Lightly grease a 9x13 inch baking dish. Cook pasta according to package directions. Drain.
Meanwhile, in a large saute pan, melt the butter. Add the garlic and red pepper and cook until tender, 3-5 minutes. Stir in the flour and cook a few minutes more.
Whisk in the half-and-half and chicken stock. Cook and stir until sauce is bubbly and thickened. Stir in the taco seasoning, cumin, oregano, and cayenne pepper. Season with salt and pepper, to taste.
Add 2 cups of the cheese and stir until melted. Stir in the chicken, corn and green onions and mix well.
Transfer the pasta to the prepared baking dish. Top with remaining cheese. Bake, uncovered, for about 30 minutes, or until pasta is bubbly and cheese is golden. Top with fresh chopped cilantro before serving.