Place the dry couscous in a small heat-proof bowl and pour the boiling water over it; cover tightly and let sit for 5 minutes.
Trim any excess fat from the lamb leg and cut into 1-inch cubes.
In a small bowl, combine the ground cumin, coriander, cinnamon, sea salt, and black pepper, then toss the lamb chunks in the spice blend until evenly coated.
Heat the olive oil in a large skillet over medium-high heat.
Add the spiced lamb to the skillet and sear for 3-4 minutes, turning occasionally, until browned on all sides and cooked to your desired level of doneness.
Remove the lamb from the skillet and set aside on a plate; add the diced zucchini and red onion to the same skillet.
Sauté the vegetables for 4-5 minutes until they are tender and slightly caramelized from the residual lamb juices.
Fluff the couscous with a fork and stir in the lemon juice and freshly chopped parsley.
Serve the spiced lamb and sautéed vegetables over the bed of fluffy couscous.