In a bowl, combine the olive oil, garlic, parsley, spices, lemon juice, and water. Mix the marinade well, then add the lamb pieces. Let the lamb marinate for 2 hours.

Place the marinated lamb in a clay tagine and set it over the heat for 10 minutes. Add the grated tomato and chopped onion, cover the tagine, and cook over medium heat for 30 minutes.

Add the vegetables: cut the potatoes, carrots, and zucchini into long pieces and arrange them around the tagine. Place the peas on top. Cover and cook over low heat until the lamb and vegetables are tender. Garnish with chopped parsley and serve.