Make the chipotle marinade by combining all ingredients in a blender. You'll use 1/3 cup for the marinade and save the rest to serve along side.
Pound chicken breasts between two sheets of plastic wrap or inside a large ziplock bag to an even 1/2 inch thickness. Place in a bag or glass dish with 1/3 cup of the marinade and set aside at room temperature for 30 minutes while you prepare the rest of the ingredients. (if doing this part ahead store in refrigerator up to one day)
Wrap tortillas in foil and preheat your oven to 350 degrees f.
Place foil wrapped tortillas in oven and set timer for 10 minutes.
Slice peppers into 1/2 inch strips and slice onion into 1/4 inch slices. In large skillet heat 2 Tbsp oil over medium-high heat and add onion, stirring constantly 3 minutes. Add bell peppers to onions and continue stirring 4 minutes more, until they're crisp tender. season with a little kosher salt and cracked pepper. Transfer to a platter and cover with foil to keep warm.
When timer goes off turn off the oven but leave the tortillas inside to stay warm while finishing up.
In same skillet as peppers (don't wipe clean) add another Tbsp of oil and sauté chicken breasts without crowding (you may need to do this in batches if they're very large) 3 minutes per side, turning only one time so that they develop a nice golden color. When done, remove to a cutting board. (Tent with foil to keep warm while cooking the remainder if doing this in batches)
Slice chicken into 1/2 inch strips across the grain and place on platter with vegetables.
Serve chicken and vegetables with tortillas, guacamole, additional chipotle dressing, sour cream, cotija cheese, lime wedges and lots of napkins
