In a bowl, toss the chicken chunks with the fajita seasoning until evenly coated; set aside.
Heat 1 teaspoon of olive oil in a cast iron skillet over medium-high heat until shimmering.
Add the chorizo and seasoned chicken to the skillet; cook, stirring often and breaking up the chorizo with a wooden spoon, until the chicken is browned and cooked through, about 6 minutes.
While the meat cooks, warm the tortillas using your preferred method (see notes).
Transfer the cooked meat to a bowl and leave the skillet on the stovetop without cleaning it to retain browned bits.
Add the remaining 1 teaspoon of olive oil to the skillet, then add the onion and bell pepper strips; cook on high heat, tossing occasionally, until they begin to soften, about 3 minutes.
Assemble the fajitas by topping each warmed tortilla with some of the meat mixture, sautéed vegetables, a spoonful of sour cream, and the chopped cilantro; serve immediately.