Season the thighs with the fajita seasoning. Don't be shy with the seasoning. Let the chicken set for 15 minutes or up to 2 hours.
Preheat a griddle or large cast iron skillet over high heat. I used a large griddle on my gas grill, but a flat top griddle, Griddler or the like will work just fine. You'll want a large surface as this recipe makes a large batch.
Also preheat your oven to 400 F. Note: Since I was using a griddle on a gas grill, I used the grill as my oven instead.
Add 2 tablespoons of butter to the griddle. Add the thighs and cook for 4 minutes per side until lightly charred and cooked to 165 F.
Remove the chicken to a platter to cool slightly then cut into small cubes.
Add remaining butter to the griddle and add the onions and peppers. Cook until lightly softened and charred, stirring often.
Add the chicken to the vegetables. Season with more fajita seasoning and stir to combine.
Add half of the cheese and mix until melted. Remove to a plate or bowl.
Slice off the top of the bread loaves and remove most of the contents. You want a completely hollowed loaves, but be careful to not poke any holes in the sides or bottoms!
Top with the remaining cheese and sprinkle with more fajita seasoning. Transfer to the oven (or a hot grill over indirect heat) and toast for 10 minutes or until the bread is lightly toasted and the cheese is melted. If you want a little color to your cheese, place the loaves under the broiler for a minute or two.
Top with chopped fresh cilantro and Mexican crema and serve!
Notes
You can substitute shredded Monterey Jack or pepper jack for the cheese.