Mix mayo and mustard in a small bowl. Spread the mayo mixture on one surface of each slice of bread.

Mix eggs, milk, and salt together in a medium bowl. Heat oil in a small frying pan (8") at medium high heat. Pour the egg mixture into a hot pan and stir frequently. As it sets, form a round pancake like shape with a spatula. When it becomes firm enough, flip and cook the other side a minute longer. Don't cook too long as it will dry out.

Place the round egg on a slice of bread and sandwich with the other bread (mayo sides in). Cut off the edges of the bread if you like, then cut in half.

Pack sandwiches and fruits and vegetables in a bento box.