Preheat oven to 375 F.

In heavy saucepan, heat 1 tsp oil over medium-high heat. Add couscous and toast in hot oil, stirring often, until slightly golden, about 5 to 6 minutes. Add stock (carefully, as it will splatter) and reduce heat to medium. Cover and cook for 9 to 12 minutes. Remove from heat and let rest, covered, for 3 minutes.

In bowl, place prawns and 2 tsp oil. Toss to coat. Spread out on baking sheet and sprinkle with 2 tsp za'atar spice. Bake in preheated oven for 5 to 7 minutes, just until they begin to curl. Remove from oven and set aside, as they will continue to cook.

In large bowl, combine remaining 3 Tbsp oil, remaining 1 tsp za'atar spice, lemon juice, and salt. Whisk to blend. Add spinach, mint, and green onions. Scatter warm cooked couscous over top. Gently toss greens and couscous together to blend evenly. Season to taste. Transfer to large serving platter and tumble prawns and pistachios over top. Serve immediately with lemon wedges and additional fresh mint.