Position a rack in the upper third of the oven; preheat to 400 degrees F. Melt the butter in a large pot over medium heat. Add the scallions and garlic and cook until softened, about 2 minutes. Sprinkle in the flour, cumin, oregano and cayenne and stir until coated. Add the chicken broth and heavy cream and bring to a simmer. Cook until slightly thickened, about 2 minutes. Stir in the salsa and remove from the heat. Stir in the chicken, white beans and 1 cup cilantro.
Butter a 3-quart baking dish. Spread one-third of the crushed tortilla chips in the bottom. Top with half of the chicken mixture. Spread another layer of tortilla chips on top and sprinkle with half of the cheese. Top with the remaining chicken mixture, tortilla chips and cheese. Cover with foil and bake 30 minutes. Uncover and bake until lightly browned and bubbling, about 10 minutes. Top with more cilantro.