Tomato and Avocado Salsa

Preparation: 

Slice each tomato to obtain 112-inch thick slices from the widest portion of the tomato, making sure to avoid the core. Spread 1 heaping tablespoon of mayonnaise on one half of the tomato slices. Top each with an onion slice, arugulo leaf and a second slice of tomato. Dip each sandwich into the beaten egg mixture and then the bread crumbs. Gently shake off any excess bread crumbs. Set sandwiches aside. In a large heavy saute pan, warm the butter and olive oil over medium heat. Slip each sandwich into the pan and fry until golden brown, about 3 minutes on each side. Remove and serve immediately. 

1/2 cup mayonnaise or whipped cream cheese     1/2 teaspoon salt  
 1 large onion, thinly sliced    1/2 cup bread crumbs, unfiavored, toasted 
 6-8 small arugula leaves, washed & patted dry     3 tablespoons unsalted butter
 2 large eggs, lightly beaten with 1 tablespoon water     2 tablespoons olive oil