Prepare the creamy jalapeño verde sauce: In a small saucepan, bring water to a boil. Add the tomatillos and jalapeño pepper and boil for 5 minutes until softened.
Drain the tomatillos and jalapeño and transfer to a blender or food processor.
Add cilantro, sour cream, lime juice, salt, and cumin to the blender. Blend until smooth and creamy. Set aside in the refrigerator.
In a small bowl, combine chili powder, cumin, smoked paprika, garlic powder, onion powder, salt, and black pepper to create the fajita seasoning.
Place the sliced chicken in a medium bowl and toss with 1/2 tablespoon olive oil and the fajita seasoning until evenly coated.
Heat a large skillet over medium-high heat and add the remaining 1/2 tablespoon olive oil.
Add the seasoned chicken to the skillet and cook for 5-7 minutes, stirring occasionally, until the chicken is cooked through and lightly browned. Remove chicken from the skillet and set aside.
In the same skillet, add the sliced bell peppers and onion. Sauté for 6-8 minutes until the vegetables are tender-crisp and slightly caramelized.
Return the cooked chicken to the skillet with the vegetables and stir to combine and heat through, about 1-2 minutes.
Warm the flour tortillas in a dry skillet or microwave until pliable.
To serve, spoon the chicken and vegetable mixture onto each tortilla, drizzle with the creamy jalapeño verde sauce, and garnish with chopped cilantro and lime wedges on the side.