Cook couscous per package directions; drain, let cool then transfer to large bowl. Heat grill on medium-high.
In second bowl, toss asparagus and snap peas with 1 teaspoon oil and ⅛ teaspoon each salt and pepper. Grill, turning or rolling once, until lightly charred and tender, 2 to 4 minutes; transfer to cutting board.
Grill haloumi until lightly charred, about 20 seconds per side; transfer to plate.
Cut asparagus into 1-inch pieces and snap peas into halves or thirds and toss with couscous, lemon zest, and juice, remaining 2 teaspoons oil and ¼ teaspoon each salt and pepper. Fold in scallion, dill, and parsley.
Tear haloumi into bite-size pieces and fold into couscous.
