Preheat oven to 500 F degrees.
Add all the meatball ingredients to a large bowl and mix well, use your hands. Shape into 1 1/2 inch balls (or as large as you wish) sticking a mozzarella cube in each meatball. You should get around 18 meatballs.
Place the meatballs in a casserole dish, then pour the cup of chicken broth over them. This will keep them from going dry and keep them moist. Bake the meatballs for 20 minutes.
In the meantime, prepare the pesto. Add all the pesto ingredients (minus the olive oil) to a blender, and pulse for about 10 seconds, with the motor running pour in the olive oil in a slow stream until emulsified. You will not be using all this pesto, see notes for how to store leftovers.
Cut the ciabatta buns in half crosswise then toast them only on the inside, not the crust side, on a grill or under the broiler until golden.
To assemble the subs, spread some of the pesto on each bottom part of the bun, then spoon about 3 tablespoons of marinara sauce, sprinkle with some mozzarella cheese. Add 3 meatballs, 3 more tablespoons of marinara sauce, then more mozzarella cheese. Spread some more pesto over each top part of the ciabatta bun, before placing on top of the subs. You can place these in the oven for about 3 to 5 minutes at 400 F degrees until the sauce warms up and cheese melts.