Pre-heat oven to 400°F. Bring a large heavy-bottomed pot of water to a boil. Cook the pasta according to the package directions until al dente. Drain and rinse with cool water and set aside.

Dry the pot and add the butter over medium heat. Add the chopped onion and jalapeño and cook, stirring occasionally, until softened, about 6 minutes. Add the flour and salt, and cook, stirring occasionally, until the flour has darkened slightly in color, about 2 minutes. While whisking constantly, slowly add the milk to the flour mixture until evenly combined and smooth. Cook, stirring occasionally, until the mixture comes to a simmer and thickens slightly, about 8 to 10 minutes. Add the salsa and cheeses and stir until completely melted and the sauce is smooth. Stir in the pasta, pickled jalapeños and green chiles and stir to combine. Taste and season with salt and pepper as needed.

Transfer the mixture to a 13-by-9-inch baking dish and spread into an even layer. Sprinkle with the crushed TOSTITOS® tortilla chips and bake until bubbling around the edges, about 20 minutes. Remove and let cool for 5 minutes before serving. Garnish with cilantro and green onions before serving.