Step 1
Cut chicken wings at joints, separating flats, drumettes, and tips. Discard tips. Set aside 8 remaining chicken pieces. Stir together garlic, mustard, honey, and lemon zest and juice. Whisk in oil until emulsified. Whisk in pepper and 1 teaspoon of the salt.
Step 2
Place chicken in a large bowl. Add 3/4 cup garlic-lemon mixture (reserving remaining mixture in a separate bowl); toss to coat. Cover bowl with plastic wrap; chill 1 hour.
Step 3
Meanwhile, bring a large pot of water to a boil over high. Add couscous, and return to a boil. Reduce heat to medium. Simmer, stirring occasionally, until couscous is tender, about 10 minutes. Drain; transfer to a large bowl. Cool 10 minutes. Add remaining 3/4 cup garlic-lemon mixture to couscous; toss to coat. Cover; chill until ready to serve or up to 1 day.
Step 4
Preheat a gas grill to medium (350°F to 400°F). Using tongs, transfer chicken from marinade to a plate, letting excess drip off (discard marinade). Sprinkle evenly with 1/2 teaspoon of the salt. Using tongs, transfer chicken to unoiled grates, skin sides down. Grill, uncovered, until a thermometer inserted in thickest portion of thighs registers 165°F (13 to 14 minutes per side for legs and breasts and 10 minutes per side for wings). Add lemon halves, cut sides down, to grates while chicken cooks; grill until charred, 2 minutes. Let chicken rest 10 minutes.
Step 5
Stir cucumbers, parsley, mint, and remaining 1/2 teaspoon salt into couscous mixture. Divide couscous, chicken, and charred lemons among 4 plates.