Pour tequila, lemon juice and agave nectar into a cocktail shaker. Fill with ice and shake for 15 to 20 seconds.
Pour cocktail into a Collins or highball glass filled with ice. Top off with seltzer water.
Garnish with a Maraschino cherry and lemon slice.
Notes
* Before squeezing the lemon, heat it in a microwave for about 20 seconds and then rub it back and forth on the counter top. This easy two-step process results in more juice per piece of fruit.