Preheat oven to 350°F.
Drizzle the chicken breasts with olive oil and sprinkle with salt and pepper. Place on a baking sheet and bake in oven for 30 minutes, until just cooked. Let cool slightly. Use two forks to shred the chicken.
Heat oil over medium-low heat. Add onions and bell peppers and cook for 5-7 minutes, until translucent. Add the garlic and cook for 1 more minute.
Add shredded chicken to the vegetables then add cumin, chili powder, and red pepper flakes. Let cook 1-2 minutes.
Add both cans of diced tomatoes, tomato paste and 1 cup of chicken stock to the pot. Bring to a boil. Once boiling, add 1 more cup of chicken stock. Stir and simmer, uncovered, for 30 minutes. Serve and top with your favorite toppings, or refrigerate and reheat gently before serving.