Place the chocolate in a small microwave-safe bowl. Melt it in the microwave, in two or three 30-second sessions, stirring after each session.
Mix in the avocado oil and stevia.
Using a pastry brush, paint the top side of the mint leaves with the melted chocolate, as shown in the video below.
Place the leaves on wax paper and allow them to set at room temperature for about an hour.
Video
Notes
The sweetener is optional. I use it because I tend to use extra-dark chocolate. But if you don't mind the slight bitterness of extra-dark chocolate, or if you're using sweeter chocolate, you can leave the sweetener out. If you do add a sweetener but prefer to use something other than stevia, I recommend opting for a liquid sweetener, as a granulated sweetener could cause the chocolate to feel grainy.