Preheat oven to 400°F (200°C).

Thaw, drain, and squeeze the spinach dry.

Chop the onion and scallions.

Sauté spinach, onion, and scallions in butter over medium heat until tender.

In a large bowl, combine the sautéed spinach mixture, ricotta, feta, cream cheese, olive oil, eggs, parsley, and mint.

Season the mixture with salt and pepper to taste.

Mix water, lemon juice, vegetable oil, salt, and flour to form the phyllo dough.

Knead the dough until it forms a ball and does not stick to fingers, adding more flour if needed.

Roll the dough out as thinly as possible using a rolling pin or pasta machine.

Grease a 9x13-inch glass baking dish.

Line the baking dish with phyllo dough, using at least 3 layers on the bottom, buttering between each layer.

Ensure the phyllo layers cover the sides of the dish and hang over the edges.

Add the spinach and cheese filling to the baking dish.

Fold the hanging phyllo layers up and over the filling.

Add 2 or 3 more layers of phyllo over the top of the mixture, buttering between layers.

Brush the top layer of phyllo with beaten egg.

Sprinkle sesame seeds evenly over the top.

With a sharp knife, cut squares through just the top phyllo layer.

Bake for 45 minutes to an hour, or until golden brown.

Let cool slightly before cutting and serving.