Bring a pot of water to a boil. Cook the macaroni in the boiling water until just undercooked. Drain and set aside.
Meanwhile, heat the olive oil in a large cast-iron skillet over medium-high heat. Add the red onion and corn and season with salt and pepper. Cook, stirring, until the onion turns golden brown and the corn begins to blister, 4 to 5 minutes. Stir in the green chiles to combine. Set aside.
To make the sauce, melt the butter in a large pot over medium heat. Sprinkle in the flour, whisking to combine. Let the roux cook for a minute or so, whisking constantly. Pour in the milk, whisking constantly, followed by 2 teaspoons salt and 1 teaspoon pepper. Cook the white sauce until thick and bubbly, 3 to 5 minutes. Add the half-and-half and adobo sauce. Add the processed cheese, 1 cup of the Monterey Jack and 1 cup of the pepper jack and continue to cook, stirring, until the cheese all melts. Add the cooked macaroni and stir to coat. Fold in the diced tomatoes and chiles.
Butter a 9-by-13-inch disposable foil pan. Layer with half of the macaroni mixture, then half the corn mixture. Repeat the layers, ending with the corn mixture. Sprinkle the remaining 1 cup Monterey Jack and 1 cup pepper jack over the top. Sprinkle the crushed tortilla chips all over the cheese, then sprinkle with chili powder.
To bake immediately, preheat the oven to 375 degrees F. Bake until bubbly and hot, 20 to 25 minutes. Sprinkle over the chopped cilantro and serve.
To freeze the casserole for later, let cool completely, then cover with aluminum foil, fold over the edges to seal and freeze.
If cooking from frozen, preheat the oven to 375 degrees F.
Cook, covered, for 50 minutes, then uncover and bake until light brown and bubbly, about another 20 minutes. Sprinkle over the chopped cilantro and serve.
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