Preheat the oven to 375°F.

Place the pie crust in a 9-inch pie plate and crimp the edges if needed.

For a sturdier bottom crust, prick the crust with a fork and bake for 7–8 minutes before filling.

Thinly slice the zucchini, tomatoes, and onion.

Lay the tomato slices on paper towels, sprinkle lightly with a pinch of the salt, and let sit for about 10 minutes.

Blot the tomatoes dry to remove excess moisture.

Heat the olive oil in a skillet over medium heat.

Add the zucchini and onion and cook for 5–6 minutes, until slightly softened.

Season the zucchini mixture with the remaining salt, black pepper, and Italian seasoning.

Spread the cooked zucchini and onion mixture into the pie crust.

Layer the tomato slices over the top.

In a small bowl, stir together the mozzarella, mayonnaise, and Parmesan cheese until thick and combined.

Gently spread the cheese mixture over the vegetables.

Bake for 30–35 minutes, until the topping is golden and bubbly and the crust is cooked through.

If the crust edges brown too quickly, cover them loosely with foil.

Let the pie rest for 10–15 minutes before slicing.

Serve warm or at room temperature.