Remove the bones and skin from the salted salmon and cut into 1.5cm wide pieces.

Slice the onion thinly.

Heat salad oil in a frying pan over medium heat, add the onion and sauté until softened. Add the salmon, frozen spinach, and salt and pepper, and cook for about 2 minutes. Let cool.

In a bowl, mix all the egg mixture ingredients together.

Arrange the sandwich bread in a heatproof dish, slightly overlapping. Cover with plastic wrap and press down to shape the bread to the dish.

Spread the sautéed mixture evenly over the bread and pour the egg mixture on top.