In a large bowl, whisk together the flour, baking powder, oregano, black pepper and salt. Add melted butter, eggs, sour cream, buttermilk, mayonnaise, chopped onion and tomatoes. Mix well with a spoon.
Fold in cheese. Spray a 9x5 bread pan with cooking spray. Add your bread mixture. Bake in preheated 350 degree oven 60 - 65 minutes checking to see if bread is done since ovens vary.