Cook the Chicken
Place chicken in a pot with lightly salted water. Simmer until fully cooked, about 15–18 minutes. Remove, cool slightly, then shred.
Sauté the Onions
Heat oil in a large skillet over medium heat. Add sliced onion and cook until soft and lightly golden.
Build the Sauce
Add garlic and cook until fragrant. Stir in tomatoes, chipotle peppers, adobo sauce, oregano, cumin, salt, and pepper. Simmer for 10 minutes.
Combine
Add shredded chicken to the sauce and stir until fully coated. Simmer gently for another 5–10 minutes.
Serve
Taste and adjust seasoning. Serve hot with desired toppings.