Pound chicken breasts to ¾ inch thickness.
Season both sides with salt and pepper.
Dredge in flour. Shake off excess.
Heat olive oil in large skillet over medium-high heat.
Add chicken. Do not overcrowd.
Cook 5 to 6 minutes without moving until golden.
Flip. Cook 5 to 6 more minutes until done (165°F).
Transfer to plate. Cover with foil.
Reduce heat to medium. Add butter.
Add garlic. Cook 30 seconds.
Add broth, lemon juice, zest, oregano, and red pepper flakes.
Simmer. Scrape up brown bits.
Simmer 3 to 4 minutes until sauce reduces.
Return chicken to pan. Spoon sauce over. Cook 1 to 2 minutes.
Sprinkle with parsley. Garnish with lemon slices. Serve hot.