Without peeling the onions, cut 1" off the top of each and a little off the bottom so that the onions stand upright. Reserve tops. Remove all but the outer 2 layers of each by scooping out centers with a knife or pushing them up through the top. Set shells and tops aside, finely chop centers.
Melt 3 tablespoons butter in a skillet over medium-low heat. Add chopped onions and cook until soft, about 15 minutes. Meanwhile, bring stock to a simmer in a saucepan over medium heat. Add lemon zest and apricots and cook until soft, about 10 minutes.
Preheat oven to 400*F. Add lamb and cinnamon to onions, increase heat to medium, season with salt and pepper. Cook, stirring until lamb is crumbly and just cooked through, about 5 minutes. Remove from heat. Stir in stock-apricot mixture and 2 tablespoons each parsley and mint. Cool slightly.
Spoon filling into onion shells, place in an ovenproof dish. Pile bread crumbs on top (lay onion tops alongside), dot with remaining butter. Pour 1/4 cup water into dish. Bake, basting several times, for 20 minutes, then cover with aluminum foil and bake until onions are tender, about 20 minutes. Garnish with remaining mint and parsley. Serve with onion tops and couscous, if desired.