Bring a large pot of salted water to a boil over medium-high heat and cook noodles until al dente, about 12 minutes or according to directions on the box. Drain and reserve for later.
In a large pot set over medium heat, melt butter. Add flour and whisk to combine, stirring occasionally, for about two minutes or until golden. Whisk in milk, then increase heat to high, whisking constantly as the mixture thickens and comes to a simmer. Reduce heat back to medium, add salt and American cheese. Whisk for about a minute, until American cheese is fully melted, then add Jack cheese, whisking for an additional two minutes until the sauce is smooth and velvety. Add noodles directly to the sauce, and stir with a wooden spoon for about two minutes or until the noodles have soaked up some of the sauce.
In a large pan set over medium heat, heat oil. When the oil shimmers, add bacon and sauté until cooked through but not brown, about 4 minutes. Add poblanos and let sauté in the bacon fat for about 5 minutes, until peppers are tender and the bacon is browned and crispy. Drain about half the grease before stirring the bacon and peppers into the mac and cheese. Serve immediately.