In a medium-sized bowl, combine oil, paprika, chili powder, cumin, salt and pepper. Add chicken and turn to coat evenly. Marinade in refrigerator for at least 30 minutes, or up to 1 day.
Preheat grill to medium-high heat and cook chicken, 6 to 7 minutes per side. Once cooked, transfer to a cutting board and slice.
Meanwhile, cook couscous according to package instructions (usually, bring to a boil in 1 cup water, remove from heat, cover, and let sit for 5 minutes; fluff with a fork). Add lemon zest and juice to couscous, and serve. Top with tomatoes, snap peas, basil, a pinch of salt and pepper, and sliced chicken.