Heat pan to medium heat.
Add oil and onion to pan and sauté until tender.
Add in garlic and cook for 1 minute, or until aromatic.
Toast the spices (chili powder, cumin, oregano, paprika) for 1 minute.
Add in chicken stock, tomatoes, and salt and cook for 5-10 minutes, or until somewhat reduced.
Place this mixture into a blender (wait to cool) and blend until smooth.
Add olive oil and chicken breasts to the heated pan. Cook for 4 minutes on each side until golden in colour.
Add in water and cover. Simmer for another 6 minutes. Transfer to a bowl and shred with two forks.
Add the sauce and the shredded chicken back into the pan and mix until the chicken is coated in sauce. Serve warm or cold in a tortilla or on rice with your favourite veggies/toppings.