Preheat your oven to 400°F (200°C) or heat a skillet over medium-high heat.
In a large mixing bowl, combine olive oil, lemon juice, minced garlic, lemon zest, oregano, salt, black pepper, and red pepper flakes. Whisk until well mixed.
Cut the chicken breasts into bite-sized pieces and add them to the marinade, ensuring each piece is well coated. Let it marinate for at least 10 minutes.
If using a baking sheet, line it with parchment paper or lightly grease it. Spread the marinated chicken in a single layer. If using a skillet, add the marinated chicken directly to the hot skillet.
Bake in the oven for 15 minutes, or sauté in the skillet for about 6-7 minutes on each side until the chicken is cooked through and golden brown.
Check for doneness using a cooking thermometer; the internal temperature should reach 165°F (75°C).
Once cooked, remove from heat and allow the chicken bites to rest for a couple of minutes. Garnish with fresh parsley if desired before serving.