Turn the flame to medium-high on a gas grill. Slice your grapefruit and lime in half and slice off the ends of the half. Place, flesh side down, over the flame for about 2 minutes. Flip and grill the other side, about 1 minute. Allow to cool.
Using a citrus squeezer, juice the grapefruit and lime. Set aside.
In a grill basket, place the lime wheel over indirect flame. After about 2 minutes or until charred. Flip it and do the same for the other side. Remove and allow to cool.
In a shaker with ice, combine the tequila, liqueur and juices. Shake well.
Strain into a coupe glass and garnish with the grilled lime. Cheers!