Preheat grill or grill pan to medium-high heat.
In a large bowl, combine lamb, breadcrumbs, egg, onion, garlic, cumin, paprika, cinnamon, chili flakes, salt, and pepper.
Gently form the mixture into 12 to 16 meatballs (depending on size).
Brush the meatballs with olive oil and grill for 5-7 minutes, turning occasionally, until charred and cooked through.
While the meatballs cook, prepare the couscous by adding to a heatproof bowl, then pour boiling water/broth over the couscous.
Stir gently, cover with a lid, and let sit for 5 minutes until tender and fluffy.
Fluff the couscous and stir in half the parsley, mint, and olive oil.
In a small bowl, combine yogurt, remaining lemon juice, salt, and a pinch of chili flakes for the sauce.
Assemble bowls by topping herby couscous with 3-4 meatballs, cherry tomatoes, cucumber, and fresh parsley and mint.
Drizzle with the yogurt sauce, add a dollop of feta (if using), and finish with a lemon wedge and additional herbs.