Thread marinated chicken, red onion, and bell pepper pieces onto skewers, alternating and leaving space between for even cooking.
Heat a grill pan or large skillet over medium-high heat and brush lightly with oil.
Place the skewers in the pan without overcrowding.
Cook for 10–12 minutes, turning occasionally, until the chicken is fully cooked and slightly charred.
In a small bowl, whisk together grated garlic, oregano, olive oil, red wine vinegar, salt, and pepper.
In a separate large bowl, combine tomatoes, cucumber, red onion, olives, and feta.
Pour dressing over the salad and toss gently. Top with chopped mint before serving.