In a bowl, mix olive oil, salt, and pepper. Add chicken breast and coat well. Let it marinate for 15 minutes.

Preheat the grill. Grill the marinated chicken for 6-7 minutes on each side or until fully cooked. Remove from grill and let rest. On a plate, arrange spinach, chopped tomatoes, cucumber, and crumble feta cheese. Slice the chicken and place on top.

Serve the grilled chicken sliced over a bed of fresh spinach, topped with diced tomatoes, cucumber, and crumbled feta cheese. Drizzle with olive oil for flavor. Store leftovers in an airtight container in the refrigerator for up to 2 days.