Combine chicken, beer, oregano and bay leaf in a saucepan and bring to a simmer. Cook, covered, until chicken is no longer pink inside, 15 to 20 minutes. Let cool in liquid. Drain, discard bay leaf, and shred chicken (you should have about 2 cups).
Combine the chicken and Tomatillo Sauce. Season with salt and pepper.
Tomatillo Sauce (Salsa Verde)
1 lean meat