Heat a stainless steel saucepan over medium-high heat. Add the spices and stir to toast for 2 minutes. Add the water and sugar. Stir to dissolve the sugar. Add the thyme and lemon peel, cover, reduce the heat, and let simmer for 5 minutes. After 5 minutes remove from the heat, let steep and come to room temperature. Chill before using.
To serve, fill 4 cocktail glasses with ice. Add 1/4 cup spiced simple syrup to each glass. Top with 1 ounce gin, if using and the club soda.