Slice chicken thighs into long strips about an inch wide and place in a medium bowl.
Add all marinade ingredients to the chicken and stir until well combined. Let marinate for at least 15 minutes.
Slice bell peppers and onion for cooking.
Heat a large skillet over medium-high heat and add vegetable oil.
Place marinated chicken strips in the skillet and sear for about two minutes until blackened.
Remove cooked chicken and keep warm. If needed, cook more chicken with leftover marinade.
Add more oil to the skillet and sauté peppers and onions with kosher salt and any remaining marinade.
Combine cooked chicken with sautéed veggies in the skillet.
Warm each tortilla on another skillet over medium heat.
Assemble fajitas with chicken, veggies, and desired toppings in each tortilla.