Meanwhile, brush the cut sides of the zucchini with 1 tablespoon of the lemon juice and season with salt and pepper. Grill the zucchini, cut side down, over a medium-hot fire until lightly charred, about 3 minutes. Turn the zucchini and move them to the sides of the grill. Brush the chicken breasts with 2 teaspoons of the olive oil and season them with salt and pepper. Set the chicken breasts in the center of the grill and grill until cooked through, turning once, about 10 minutes. Transfer the chicken and zucchini to a platter and let stand for 5 minutes.