You can broil the shrimp instead of grilling them, if you like, and the shrimp work as appetizers too—thread them on individual skewers and lose the couscous.
2 tablespoons harissa*
1/4 cup extra-virgin olive oil, divided
3 tablespoons lemon juice, divided
1 tablespoon lemon zest, divided
1 teaspoon ground cumin
About 1 tsp. kosher salt, divided
1 pound shelled and deveined large shrimp (26 to 30 per lb.)
1 cup couscous
4 firm-ripe tomatoes, halved
Chopped fresh mint leaves
How to Make It
Heat grill to high (450° to 550°). In a small bowl, combine harissa, 2 tbsp. each oil and lemon juice, 2 tsp. zest, the cumin, and 1/2 tsp. salt. Put shrimp in a medium bowl, toss with half the sauce (reserve the rest), and let stand 10 minutes. Thread shrimp onto metal skewers.
Prepare couscous as package directs, adding remaining 1 tsp. zest. Fluff with a fork and gently stir in 1 tbsp. oil and remaining 1 tbsp. lemon juice and 1/2 tsp. salt. Set aside.
Brush tomatoes with remaining 1 tbsp. oil. Grill shrimp and tomatoes, covered, turning once, until shrimp is opaque and tomatoes are softened, about 4 minutes. Serve with couscous plus a sprinkle of mint, more salt to taste, and remaining sauce.
*Find this North African chile-and-spice paste in the international section of supermarkets. We like Dea brand, which is medium-hot.