Poach the chicken in the chicken stock or water with the carrots, onion, bay leaf, and leek (if using) until cooked through.
Remove the chicken and shred it.
In a blender, combine the 3 cups of chicken stock, tomatoes, guajillo chilis, garlic, salt, cumin, thyme, oregano, and chipotle peppers. Blend until smooth.
In a large skillet, heat the oil over medium heat. Add the 2 medium onions and sauté until translucent.
Add the shredded chicken and the tomato-chili sauce to the skillet. Simmer for 10-15 minutes, until the sauce has thickened.
Season with salt and pepper to taste.
