In a bowl, lightly beat the eggs with milk, salt, and white pepper.

Heat the olive oil in a medium skillet over low heat.

Add the chopped onion and cook, stirring occasionally, until the onion becomes translucent, about 3 minutes.

Add the diced zucchini, salt, and pepper, and cook for an additional minute.

Cover and cook for about 4 more minutes until the zucchini is tender.

Then, uncover the skillet, add the chopped hake or cod, and cook until the fish turns white, which will take about 1 to 2 minutes.

Create a makeshift double boiler by half-filling a larger skillet with water and bringing it to a boil over high heat.

Reduce the heat to low and place the skillet with the zucchini and fish mixture into the larger skillet.

Pour the beaten eggs into the skillet with the zucchini and fish mixture.

Stir constantly with a wooden spoon until the eggs are set but still soft.

Spoon the cooked mixture onto each slice of bread.