Fill the bottom of each dessert cup with graham cracker crumbs, about 1 tablespoon. Spoon yogurt over the graham cracker crumbs, about 1/2 yogurt container into each dessert cup. Use the back of the spoon to gently press the yogurt down into the cup. In a chilled bowl, beat whipping cream until stiff peaks form. Optionally, mix in 1/2 to 1 teaspoon of artificial sweetener. Spoon whipped cream over the yogurt. Top with the zest of one lemon. Save the rest of the lemon for a pitcher of water or iced tea.