Place tomatoes, white 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. Adjust seasoning with salt and pepper.
Remove ½ of the tomato sauce from pan and place in a sauté pan. Add pulled chicken to the reserved tomato sauce in sauce pan.
Now to build the enchiladas. Place tortilla into sauté pan with warm sauce, this will make them pliable. Now add a healthy amount of chicken, roll, and place open side down into a casserole dish so the weight of the roll holds it closed. Repeat this with the remaining tortillas until dish is full. Now pour the extra sauce and any extra chicken mixture onto the rolled/stuffed tortillas. Top with cheese and place in oven for 20 minutes.
Once enchiladas are hot, remove from oven and garnish with sour cream, guacamole, cilantro leaves and red onions.
