Preparation Prepare a grill for medium heat. Zest 2 tsp. lemon zest off lemon and transfer to a large bowl. Cut off ends, then squeeze 1 Tbsp. lemon juice into bowl with zest. Slice remaining lemon into thin rounds. Whisk garlic, salt, paprika, and 3 Tbsp. oil into lemon juice and zest. Add lemon slices, chicken, leeks, bell pepper, and potatoes and toss to coat. Brush wires of grill basket with oil, then add chicken mixture. Arrange in an even layer and close basket. Place grill basket on grill, cover, and cook, turning once halfway through, until chicken is fully cooked through and vegetables are lightly charred, 20–25 minutes. Transfer chicken mixture to a large bowl, add parsley, and toss to combine.