Preheat a grill to medium. Season the chicken. Grill, turning occasionally, until juices run clear, 35 minutes.
Drizzle the cut sides of the baguette with EVOO. Grill, cut side down, covered, until crispy, about 5 minutes. Cut the bread into 1-inch pieces; place in a large bowl. Add the tomatoes, onion, cucumber, basil, feta and olives. Toss with 3 tbsp. EVOO; season.
Place the bread salad on a platter. Top with the chicken. Squeeze lemon over before serving.