Divide the grapefruit juice between the 2 glasses, then add 1 tbs agave nectar to each glass. Squeeze half of the second lime into each glass. Stir gently to combine. Fill the glass with your desired amount of ice, then pour 4 oz. tequila in each glass. Top with club soda, then sprinkle ¼ tsp chaat masala on top of each drink. Slip a citrus wedge into the side of each drink and serve immediately.