Step 1
Place 1–1¼ lb. boneless New York strip steak (1–1½” thick), cut into 1″ pieces, 1 Tbsp. dried oregano, 2 tsp. onion powder, 2 tsp. sugar, and 2 tsp. Diamond Crystal or 1¼ tsp. Morton kosher salt in a medium bowl; season generously with freshly ground pepper and toss to coat. Let sit at least 10 minutes or cover and chill up to 8 hours (no need to bring to room temperature before cooking if chilling).
Step 2
Heat 2 Tbsp. extra-virgin olive oil in a large high-sided skillet or medium Dutch oven with a tight-fitting lid over medium. Add 1 bunch scallions, thinly sliced, ½ cup finely chopped dill, 3 garlic cloves, finely chopped, and a large pinch of kosher salt; cook, stirring occasionally, until scallions are softened, about 5 minutes. Add 10 oz. baby spinach in 2–3 handfuls, stirring and letting wilt slightly after each addition before adding more, 5–7 minutes total. Pour in 1 cup water and bring to a boil; season with more salt if needed. Add 1 cup Moroccan couscous and stir to break up any lumps. Remove from heat; quickly cover with lid and let sit 10 minutes.
Step 3
Meanwhile, heat 1 Tbsp. extra-virgin olive oil in a large skillet, preferably cast iron, over high. Arrange steak in a single layer; cook, undisturbed, until deeply browned underneath, 6–8 minutes. Reduce heat to medium; continue to cook, stirring often, until meat is just cooked through, about 1 minute more. Remove from heat. Add remaining 3 garlic cloves, finely chopped, and a large pinch of kosher salt; toss to combine. (Residual heat from pan will cook out any raw garlic flavor.)
Step 4
Uncover couscous and fluff with a fork to separate grains. Spoon into a large shallow bowl or onto a platter. Top with steak. Cut 1 lemon into quarters and squeeze juice from 1 quarter over steak. Scatter thinly sliced cucumber and some dill sprigs on top; drizzle with oil.
Step 5
Combine 1 cup plain whole-milk yogurt and a generous pinch of kosher salt in a small bowl; squeeze juice from 2 lemon quarters into yogurt. Stir to combine. If sauce is thick, stir in water, a spoonful at a time, to loosen.
Step 6
Serve steak and couscous with yogurt sauce and remaining lemon quarter and more lemon wedges for squeezing over.
