Add cherry tomatoes, couscous, harissa, olives, and chili flakes; cook for 5 minutes, then add water and simmer until couscous is tender, about 10 minutes.
Return salmon to the skillet, drizzle with lemon juice, and cook for 2-3 minutes to reheat. Garnish with pistachios and parsley before serving.
Notes
For extra flavor, add a squeeze of lemon before serving.