Cook the macaroni pasta, following the package instructions.
Meanwhile, in a large saucepan, cook the beef and onion over medium heat until the meat is no longer pink, breaking it into crumbles.
Add the garlic and cook for one additional minute.
Drain off any excess grease.
Stir in the tomatoes, beans, tomato paste, chiles, salt, chili powder, cumin and pepper.
Bring to a boil, then reduce to a simmer and cook, uncovered, for 10 minutes.
Drain the macaroni and stir it into the beef and tomato mixture.
Preheat the oven to 375°F.
Split the macaroni mixture between two greased 2-quart baking dishes.
Sprinkle with cheese and sliced jalapenos.
Cover the casseroles and bake for 30 minutes.
Remove the covers and bake until they're bubbly and heated through, about 10 minutes longer.
