Cook the whole wheat penne pasta according to package instructions until al dente. Drain and set aside.
In a small bowl, combine chili powder, ground cumin, smoked paprika, dried oregano, cayenne pepper, salt, and black pepper. Mix well to create the fajita seasoning.
Heat olive oil in a large skillet over medium-high heat. Add the chicken strips and sprinkle half of the fajita seasoning over the chicken. Cook for 5-6 minutes, stirring occasionally, until the chicken is cooked through and lightly browned. Remove the chicken from the skillet and set aside.
In the same skillet, add the sliced onions and bell peppers. Sprinkle the remaining fajita seasoning over the vegetables. Sauté for 5-7 minutes until the vegetables are tender-crisp.
Add the minced garlic to the skillet with the vegetables and cook for 1 minute until fragrant.
Pour in the chicken broth and bring to a simmer. Let it cook for 2-3 minutes to reduce slightly.
Reduce the heat to low. Stir in the Greek yogurt and shredded cheddar cheese until the sauce is creamy and smooth. Do not boil after adding yogurt to prevent curdling.
Return the cooked chicken to the skillet and mix well to coat with the sauce and vegetables.
Add the cooked pasta to the skillet and toss everything together until well combined and heated through.
Remove from heat and sprinkle chopped fresh cilantro on top before serving.