Combine the honey and hot water. Whisk to combine.
Place the lemon halves, cut side down, on either a grill or a skillet over medium-high heat. Add the lemon wheels. Cook until the flesh of the lemons is browned. Set aside to cool.
Once cooled, juice the grilled lemon halves.
Rim two glasses with sugar or kosher salt, depending upon your preference. Add ice to the glasses. Set aside.
Add the grilled lemon juice, mezcal, lime juice, and honey syrup to a cocktail shaker with ice. Shake until very cold. Strain into the prepared glasses.
Add a grilled lemon wheel to each glass. Garnish with a sprig of fresh rosemary.
Notes: Meyer lemons would be great in this cocktail, too.