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 them. 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. Cook for 5-7 minutes, stirring frequently, until the vegetables are tender-crisp.
Add the minced garlic to the skillet with the vegetables and cook for 1 minute until fragrant.
Return the cooked chicken to the skillet with the vegetables. Pour in the chicken broth and bring to a simmer. Let it cook for 3-4 minutes to reduce slightly.
Remove the skillet from heat and stir in the Greek yogurt until the sauce is creamy and well combined.
Add the cooked pasta to the skillet and toss everything together until the pasta is evenly coated with the sauce.
Sprinkle the shredded cheddar cheese over the pasta and cover the skillet for 2 minutes to allow the cheese to melt.
Garnish with chopped fresh cilantro before serving.