Cook pasta in salted boiling water until al dente.
Whisk eggs with Pecorino Romano and Parmesan cheese until smooth.
In olive oil, fry diced bacon or pancetta until crispy; remove and set aside.
Add chicken to the bacon fat and cook until golden and fully cooked.
Stir in minced garlic and cook for about 30 seconds until fragrant.
Return bacon to pan, reduce heat, and add the drained hot pasta.
Remove pan from heat and toss everything together quickly.
Pour in egg-cheese mixture, stirring constantly; add pasta water gradually.
Season with black pepper and salt to taste.
Garnish with parsley and reserved bacon bits before serving.