In a large bowl, whisk together the olive oil, lemon juice, minced garlic, oregano, salt, black pepper, and red pepper flakes (if using).
Add the chicken cubes to the marinade, ensuring they are well coated. Cover and refrigerate for at least 30 minutes, or up to 2 hours for more flavor.
Preheat your grill to medium-high heat. If using wooden skewers, soak them in water for 30 minutes to prevent burning.
Thread the marinated chicken onto the skewers, leaving a little space between each piece for even cooking.
Place the skewers on the grill and cook for about 10-12 minutes, turning occasionally, until the chicken is cooked through and has nice grill marks. The internal temperature should reach 165°F (75°C).
Remove the skewers from the grill and let them rest for a few minutes. Garnish with chopped parsley and serve with lemon wedges.