Heat the grill to medium-high heat.
Using a sharp knife, cut a pocket in the chicken breasts, being careful not to cut all the way through.
In a mixing bowl, add the bell peppers, onions, 1 tablespoon fajita seasoning, 1 tablespoon canola oil, and a pinch of salt. Mix until everything is coated evenly.
Stuff each chicken breast with some of the peppers and onions. Close the opening of each chicken breast with toothpicks.
Season both sides with salt and pepper. Mix the remaining canola oil and fajita seasoning in a small bowl. Brush both sides of each chicken breast with the mix to completely coat them.
Grill the chicken 6-8 minutes on each side or until the internal temperature reaches 165°F. It's okay to turn them more than once. There's no rule that says you can't.
Let the chicken rest about 5 minutes before cutting. Slice each chicken breast and place 2 or 3 slices on a tortilla. Assemble with the toppings of your liking.
You can click here to read the post and get the recipe: Fajita Seasoning Spice Blend.
Prepare Ahead. This is a meal that is simple to prepare ahead of time, and it's a really good idea. Follow the steps 1-5 then place them on a plate, tray, or other container, cover with plastic wrap, and place it in the fridge. You can do this a couple hour to a day or 2 beforehand. You can even freeze them whole for later use.
For freezing premade stuffed chicken breasts or whole cooked breasts, place them on a sheet pan lined with parchment paper to freeze them individually. After about 3 hours, you can take them off the sheet pan and store them in the freezer in a freezer bag or airtight container for up to 6 months.
Bell Peppers - I like colorful food, so I tend to use yellow, red, and green bell peppers. But this is not required. You can use whichever colors you like or even just one.
Fajita Seasoning - I use my own blend which the recipe is included here. But you can use your own or a store bought one you like.
Flour Tortillas - most restaurants use 8-inch flour tortillas, and I do too. You can use larger ones or you can use ones that fit a dietary requirement you have or prefer.
Shredded Cheddar Cheese - my favorite is to shred my own extra sharp cheddar from a block. But pre-shredded will work just fine.
Pico De Gallo - here is a link to my recipe: Pico de Gallo
Guacamole - here is a link to my recipe: Mexican Style Guacamole