Wash and dry all produce. Bring stock concentrate and 1 cup water to a boil in a medium pot. Core and seed bell pepper, then thinly slice. Mince or grate garlic. Trim scallions, then separate whites from greens. Thinly slice whites. Finely mince greens. Zest lemon until you have 1/2 tsp zest, then cut into halves.

Once liquid is boiling, add couscous to pot. Cook, uncovered, until al dente, 10-11 minutes.

Meanwhile, heat a drizzle of oil in a large pan over medium-high heat. Add bell pepper and cook, tossing, until softened, 4-5 minutes. Add scallion whites and garlic to pan. Cook until fragrant, 1 minute longer. Season with salt and pepper. Remove from pan and set aside.

Pat steak dry with a paper towel. Season all over with cumin, salt, and pepper. Heat another drizzle of oil in same pan over medium-high heat. Add steak and cook to desired doneness, 4-7 minutes per side. Remove from pan and set aside to rest.

Add veggie mixture, spinach, lemon zest, and a drizzle of oil to pot with couscous. Season to taste with salt and pepper. In a small bowl, mix scallion greens, a large drizzle of oil, and a squeeze of lemon juice. Season to taste with salt and pepper.

Thinly slice steak against the grain. Divide couscous salad between plates. Top with steak and scallion dressing.