Season the beef with kosher salt and let sit at room temperature for 1 hour.
Sauté the onion in oil until starting to brown, then add the garlic, bay leaves, and oregano and cook for 30 seconds.
Add enough beef stock to just cover the onions, then nestle the beef on top. Add the peppercorns.
Bring to a simmer, then transfer to a 300°F oven for 2-4 hours, shuffling the beef every 45 minutes.
Toast the chiles in a dry pan for 3-4 minutes until fragrant, then cover with water and add the onion and garlic. Steep for 30 minutes, then blend until smooth.
Make a roux with the oil and flour, then whisk in the stock and chili puree. Simmer for 5-15 minutes until thickened.
Poach the chicken breasts in the hot water bath for 15 minutes until cooked through.
Broil the jalapeños, poblanos, and tomatillos until charred, then blend with the cilantro, salt, and pepper.
Sauté the onion, zucchini, and roasted poblano until lightly caramelized.
Toast the corn tortillas over an open flame until charred and pliable.
Assemble the enchiladas by dipping the tortillas in sauce, filling, and rolling tightly. Arrange in a baking dish, top with sauce and cheese, and bake at 375°F until bubbly and browned.
Garnish with crumbled cheese, lime zest, and cilantro.
