Rub the rim of a glass with half a lime, then dip into salt. Add ice to the glass.
In a shaker add the basil leaves, chile and lemon juice. Using a muddler, muddle intensely until the basil is mashed. Incorporate the mango nectar, tequila, agave syrup and ice. Shake until well mixed.
Pour into the rimmed glass with ice. Garnish with a mango slice and basil leaf.