Cook cauliflower rice in microwave according to package instructions. Once cooked, set aside.
Meanwhile, in a mixing bowl, whisk together grated Parmesan, Italian seasoning, garlic powder, smoked paprika, salt, and pepper. One at a time, add chicken to bowl and coat in Parmesan and seasoning mixture. Shake off excess and transfer to a plate. Do not discard remaining Parmesan and spice mixture.
To a large pan over medium-high heat, add avocado oil. Once hot, place chicken in pan and cook until each side is golden and internal temperature reaches 165 degrees, about 5-7 minutes per side, depending on thickness of chicken. Using tongs, transfer cooked chicken to a separate plate and set aside.
In same pan over medium-low heat, melt butter. Add minced garlic and chopped onions and cook until fragrant, about 1 minute. Increase stovetop heat slightly, add steamed cauliflower rice then remaining Parmesan and spice mixture and stir until ingredients are well-incorporated, and cook for 1 minute. Add in lemon zest and cook for additional 1 minute before pouring in lemon juice.
Add chicken back to pan and cook for 1-2 minutes. Garnish with parsley, grated Parmesan, red pepper flakes, and pepper and serve.