Meanwhile, in a big, deep pot, brown beef in oil over medium high heat. Add onions, peppers, and garlic. Season meat mixture with chili powder, cumin, cayenne, and salt. Cook together 5 minutes, stir in beer or broth, and reduce liquid by half, 2 minutes. Stir in tomatoes and simmer for 10 minutes.
Drain pasta. Add hot pasta to chili pot and stir to coat pasta evenly. Remove from heat and garnish big bowlfuls of chili mac with chopped scallions.