In a medium bowl, whisk together the eggs. Whisk in the flour, cornstarch, sparkling water, and salt; set aside.
In a small bowl combine the goat cheese, shredded mozzarella, and salt. Stir together until smooth. Carefully spoon 1 1/2 - 2 teaspoons filling into each blossom. Add a cube of mozzarella into the filling and gently twist the blossoms to seal it around the filling.
You could also add the filling mixture to a zip locked or piping bag. If using pastry bag (or zipped lock bag with corner cut off), pipe about two tsp. cheese mixture into each zucchini blossom.
Twist the petals at the top to keep the filling from spilling out during frying.
In a large frying pan, heat enough oil to cover the bottom (oil should reach 350F).
When oil is hot, dip each stuffed blossom in the batter, letting any excess batter drip off.
Add the blossoms to the pan, without crowding them, and fry 2-3 minutes each side until they are golden brown, turning occasionally.
Place the blossoms on a paper tile lined dish or baking sheet to drain. Enjoy while they’re hot!