In a large bowl, whisk together olive oil, lime juice, minced garlic, chili powder, ground cumin, smoked paprika, dried oregano, salt, and black pepper to create the marinade.
Add the thinly sliced chicken breasts to the marinade and toss to coat evenly. Cover and refrigerate for at least 2 hours or overnight for best flavor.
In a separate large container or bowl, combine the sliced red, yellow, and green bell peppers with the sliced onions. Cover and refrigerate until ready to cook.
When ready to cook, heat a large skillet or grill pan over medium-high heat.
Add the marinated chicken in a single layer and cook for 5 to 7 minutes, stirring occasionally, until the chicken is cooked through and slightly charred. Remove chicken from the pan and set aside.
In the same pan, add the sliced bell peppers and onions. Cook for 7 to 10 minutes, stirring frequently, until vegetables are tender and slightly caramelized.
Return the cooked chicken to the pan with the vegetables and stir to combine. Cook for an additional 2 minutes to heat through.
Warm the flour tortillas in a dry skillet or wrapped in foil in the oven.
To serve, spoon the chicken and pepper mixture onto warm tortillas. Garnish with chopped fresh cilantro and serve with sour cream, shredded cheddar cheese, and guacamole on the side.