Heat the olive oil in a large casserole over a medium flame. Add the lamb chunks in batches and brown well on all sides. Remove and set aside while you finish the remaining lamb. After all the lamb has been browned return it to the pot. Combine the coriander, cumin, turmeric and cardamom in a bowl and sprinkle the lamb with the spice mix. Brown the spice coated meat over low heat being careful not to burn the spices. Season with the salt and pepper.
Add the vegetable to the pot and stir to combine well. Add the water and bring quickly to a boil. Reduce the heat and cook for 1 1/2 hours or until the lamb is fork tender.
Combine the fresh herbs in a bowl with the red pepper, lemon juice and tomato. Adjust the seasoning and set aside.
Cook the couscous according to package directions.
Remove the stew from heat and stir in the fresh herbs and tomato. Serve over couscous.