Heat a large skillet over medium-high heat with 1/2 tablespoon olive oil. Once hot, add the ground chicken and brown one side for 3-4 minutes before flipping and pushing to one side of the pan.
Add the remaining tablespoon of olive oil, followed by the onion, celery, bell pepper, garlic, and cajun seasoning. Stir everything together with the chicken and cook until the chicken is fully cooked.
Add the orzo, hot sauce, lemon juice, and chicken broth, stirring everything together. Continue cooking, stirring occasionally, until the orzo is cooked and little liquid remains, about 12 minutes. (Add 1/4 to 1/2 cup of broth if needed.)
Turn off the heat and stir in the milk, parmesan, and herbs. Top with the cheddar cheese and cover to melt or place under the broiler for 3-5 minutes. Serve with fresh lemon juice and additional hot sauce, if desired.