Cut 1 lemon in half. From remaining lemon, finely grate 1 teaspoon zest and squeeze 4 tablespoons juice. Cut chicken into 1 1/2-inch chunks; thread onto skewers and season with 1/4 teaspoon each salt and pepper. Grill until cooked through, 3 to 4 minutes per side. Grill 1 lemon half, cut side down, until charred; squeeze over chicken. Grill bread until toasted, rub both sides with garlic halves, then cut into cubes. In a large bowl, whisk together lemon zest and juice, egg yolk, mustard, grated garlic and 1/2 teaspoon salt. Slowly whisk in oil. Fold in Parmesan, then kale and croutons, and season with pepper. Serve with chicken.