Swapping half the pasta for canned cannellini beans gives this riff on stove-top macaroni and cheese a good punch of protein. Fresh chorizo and pepper jack cheese add wonderful heat while scallions lend a bite of freshness.
Fill a large saucepan two-thirds full of water and bring to a boil, then add a small handful of salt. Add the pasta shells and cook until al dente. Drain in a colander.
In a deep 12-inch broiler-safe skillet, heat the olive oil until shimmering. Add the chorizo and cook over medium-high heat, breaking up the meat with a wooden spoon, until browned and cooked through, about 7 minutes. Add the butter and cook, stirring, until melted. Sprinkle the flour evenly on top and cook, stirring, until bubbling, about 2 minutes.
Gradually whisk in the milk until smooth. Simmer over medium-low heat, stirring occasionally, until thickened and no floury taste remains, 5 to 7 minutes. Remove the skillet from the heat.
Gradually fold the cheese into the sauce until melted, then stir in the mustard, garlic powder and onion powder. Season the cheese sauce with salt and pepper. Gently fold in the cooked pasta, beans and half of the scallions. Scatter the panko evenly over the beanaroni and cheese.
Position an oven rack 6 to 8 inches from the broiler unit and preheat the broiler to high. Broil the beanaroni and cheese until the panko is browned, 1 to 2 minutes. Garnish with the remaining half of the scallions and serve.