Cook spaghetti according to package directions; strain and set aside.
Clean and slice the chicken thinly or pound to tenderize. Add the flour to a shallow dish and season with salt and pepper. Place the chicken into the flour mixture and coat all surfaces; pat off excess flour. Heat a sauté pan with 3 tbsp. olive oil and 1 tbsp. butter. Pan sear the chicken for 5 to 6 minutes over medium high temperature. Add the onions and garlic and cook for 2 to 3 minutes. Lower the heat to medium low and deglaze the pan with lemon juice, wine, chicken stock or broth and 3 tbsp. capers.
Rinse and pat dry 2 tbsp. capers. Heat 2 tbsp. of olive oil in a separate frying pan over medium high heat; add capers and cook until crispy, about 2 to 3 minutes. Remove from oil, drain on paper towels or fine screen; set aside.
Remove chicken from the sauté pan, leaving the sauce behind. On low heat, add 1 tbsp. butter and parsley to the sauce. Heat the mixture until it thickens to your desired consistency.
To serve, plate pasta then layer with chicken and butter-garlic sauce. Top with crispy fried capers, grated parmesan cheese and lemon zest, if desired.