In a medium saucepan over medium heat, melt the butter. Add onion and saute until onion is soft and translucent, about 5 minutes. Add olive oil, bread crumbs, salt and pepper and cook for 2-3 minutes until bread crumbs are well combined and golden. Remove from heat and add 1/2 cup Parmesan cheese and mix well. Set aside.

Preheat oven to 375 degrees. Line a baking sheet with aluminum foil and spray with non-stick spray.

Slice the top off the tomatoes and scoop out and discard the flesh and liquid. Fill each tomato with the onion, cheese and breadcrumb mixture. Place the tomatoes on the baking sheet. Sprinkle Parmesan cheese over the top of each tomato and drizzle with olive oil. Bake for 30 minutes.