Start with ⅓ of the olive oil over medium heat in the tagine base on the stovetop. Once the oil is hot, add in the chopped onion and sauté until translucent. Toss in minced garlic and sauté for another minute before lowering the heat to low.
In a small bowl combine remaining olive oil, minced parsley, cilantro, preserved lemon, and ras el hanout. Mix well and set aside.
Preheat oven to 350. In the base of the tagine, start arranging the sliced potatoes and artichoke hearts over the onions and garlic. Next add the olives and peas. Drizzle the olive oil mixture over top before pouring the water over everything.
Cover the tagine and bake for an hour or until the potatoes are cooked through. Serve over a bed of couscous or with a warm piece of bread.