Preheat oven to 350°F.
Place tomatoes, onion, peppers, garlic, cilantro stems and chili powder into a blender. Pulse until you have a smooth puree.
Add tomato mixture and stock to a medium sauce pan and cook on medium for 10 minutes.
Add chicken and cook for another 10 minutes. Adjust seasoning with salt and pepper.
Place tortillas on a baking sheet and warm in oven for 2 minutes.
Remove tortillas from oven, top with chicken and then garnish with sour cream, cheese, and cilantro leaves.
Serve with lime wedges and enjoy with your favourite hot sauce.