Make sure you have thawed the fillo before starting. Either thaw the fillo overnight in the refrigerator or for 2-3 hours on the counter.
In a medium bowl, toss the shredded zucchini with about 1 tablespoon of kosher salt and let it sit for 1 hour. Leaving the liquid behind, transfer the zucchini to a towel and squeeze tightly until the zucchini is fairly dry.
While the zucchini is resting in the salt, heat the tablespoon of olive oil in a small saute pan. Add the onion, garlic, and a sprinkle of kosher salt and saute until soft, about 5 minutes. Set aside.
Pour the liquid out of the medium bowl. Add the squeezed zucchini, reserved onion and garlic, the chopped herbs, crumbled feta, fontina, and eggs. Grind a few turns of black pepper over all and then mix well.
Preheat the oven to 350F.
Take out your 9-inch springform pan. Unroll the fillo dough next to the pan and cover it with a kitchen cloth. Either set out a bottle of spray olive oil or put some olive oil into a cup with brush.
Once you are organized, it's time to layer the fillo.
Take a sheet of fillo and coat it lightly, but thoroughly, with oil. Put the sheet into the pan tucking it into the bottom and bottom edges of the pan. Repeat with 2-3 more fillo sheets.
With the next sheet, arrange it so that it overhangs one side of the pan by about 2 inches with the rest of the sheet tucked into the bottom. Continue, turning the pan a little each time, layering in sheets to overhang until you have fillo overhanging all around.
Spoon the zucchini filling into the pan, smoothing it down into an even layer. Fold the fillo edges up over the filling so that the fillo is wavy and folded.
Bake the zucchini pie for 45-50 minutes, or until the fillo is golden brown and the filling is full set.