Prepare the Lemon Curd:**
- In a medium saucepan, combine the lemon juice, lemon zest, sugar, and egg yolks. Cook over medium heat, whisking constantly until the mixture thickens, about 5-7 minutes. It should be thick enough to coat the back of a spoon.
- Remove the saucepan from the heat and whisk in the cubed butter until the curd is smooth and creamy.
- Transfer the lemon curd to a bowl, cover with plastic wrap directly on the surface to prevent a skin from forming, and refrigerate until completely chilled.
**Fill the Cannoli Shells:**
- Once the lemon curd has chilled, spoon it into a piping bag fitted with a large round tip.
- Pipe the lemon curd into both ends of each cannoli shell, filling them completely.
- Place the filled cannolis on a tray and set aside.
**Prepare the Meringue:**
- In a large, clean bowl, beat the egg whites and cream of tartar with an electric mixer on medium speed until soft peaks form.
- Gradually add the sugar, 1 tablespoon at a time, beating on high speed until stiff, glossy peaks form. Add the vanilla extract and beat until just combined.
**Top with Meringue:**
- Spoon the meringue into a piping bag fitted with a star tip.
- Pipe the meringue onto each end of the filled cannolis, creating a decorative swirl.
- Use a kitchen torch to lightly toast the meringue until golden brown, being careful not to burn the shells.
**Serve:**
- Optionally, dust the cannolis with powdered sugar for an extra touch of sweetness.
- Serve the Zesty Lemon Meringue Pie Cannolis immediately, or store them in the refrigerator until ready to serve.