Preheat oven to 450 degrees. Halve, peel, and dice onion. Pick leaves from cilantro and discard stems. Roughly chop leaves.

Heat a drizzle of olive oil in a small pot over medium-high heat. Add onion and toss until softened, 3-4 minutes. Stir in stock concentrate and 3/4 cup water and bring to a boil. Add couscous, cover, and remove from heat.

Heat a drizzle of olive oil in a large ovenproof pan over high heat. Season pork all over with salt, pepper, and half the shawarma spice. Add pork to pan and sear until browned but not cooked through, about 2 minutes per side. Transfer pan to oven and roast pork until cooked to desired doneness, 4-8 minutes.

Meanwhile, mince or grate 1/2 tsp garlic. Halve lemon. In a small bowl, combine yogurt, remaining shawarma spice, a squeeze of lemon, and a pinch of garlic (to taste). Stir in 1 TBSP water to give mixture a saucy consistency. Season with salt and pepper.

When pork is done, remove from pan and let rest 5 minutes. Place pan used for pork over low heat. Add peas and toss until heated through, 1-2 minutes. Fluff couscous with a fork and stir into peas along with a squeeze of lemon. Season with salt and pepper.

Thinly slice pork and serve on a bed of couscous. Dollop with yogurt sauce and scatter with cilantro leaves.