Using a medium sized skillet, fill about 1/4 with extra-virgin olive oil and let heat on medium-high heat.
In a medium sized bowl, combine ricotta cheese, mozzarella cheese, Parmesan cheese and spinach. Add garlic salt and mix together well with clean hands. Gently fold in the chopped tomatoes.
Meanwhile, set up breading station using a small to medium bowl for the eggs, one plate with Italian bread crumbs and another plate for the Panko crumbs. Make cheese mixture into 2-inch balls and gently pat down to a "patty"; dip the fritter into the Italian bread crumbs then dip into egg mixture. Dip the fritter into the Panko crumbs. Repeat until all tomato slices are breaded. (For better results with the fritter staying together, you may want to put these in the freezer for 10-15 minutes before doing any further).
Preheat oven to 350 degrees.
Place three to four fritters into the oil and fry for 1 to 2 minutes and gently turn over using tongs. Allow to cook for 1 to 2 minutes longer or until golden brown.
Place fritters on a baking sheet sprayed lightly with non-stick cooking spray. Bake for 15 minutes or until heated through.