Wet the rim of 2 glasses and dip in the mixture of coarse salt and chili powder. Fill a cocktail shaker two-thirds of the way with ice. Add the tequila, both sorts juice, fresh lime juice and agave nectar. Shake well, then strain into the glasses and decorate with a slice of lime.
Recipe by Box of Spice at https://boxofspice.com/2013/05/chili-pineapple-guava-margarita/