In a medium bowl, toss half of the garlic with the 2 tablespoons of olive oil and the shrimp. Preheat a grill or grill pan to medium-high. Skewer the shrimp, season with salt and pepper and grill, until cooked through, about 2 minutes on each side. Set aside.
In a microwavable dish, stir the couscous with the chicken broth and season to taste with pepper. Microwave the couscous on high for 4 minutes; fluff with a fork.
In a small bowl, stir together the lemon juice and lemon zest, the remaining garlic and the parsley. Whisk in the remaining 1/4 cup of olive oil and toss with the cucumber. Spoon the dressing over the couscous, adjust the seasoning and top with the grilled shrimp.