Preheat oven to 375 degrees F.
Line 9 1/2 inch by 13 inch baking sheet with parchment paper.
Rinse tomatoes thoroughly and slice horizontally, about one-half-inch thick. Set aside.
Working quickly but carefully, unroll phyllo dough from package and spread out onto parchment paper.
Using pastry brush, very gently sweep melted butter along all of phyllo dough from end-to-end, thoroughly coating.
Arrange tomato slices on phyllo dough in rows, leaving a one to two inch crust around all four sides of the pan.
Sprinkle the top of the tomatoes with the thinly sliced red onions.
Add the very thinly (or minced) shallots on top of the tomatoes and red onions, distributing evenly.
Sprinkle the olive oil on top of the vegetables.
Add the feta cheese.
Place baking sheet in center rack of oven and cook for 15-20 minutes, until crust turns a light golden brown.
Remove from oven and let cool for 5 minutes before cutting and serving.
