Preheat the oven to 350 degrees F.
In a large bowl combine the beef, spinach, zucchini
, onion, bulghur, egg
, oregano, salt and a few grinds of pepper. Mix until thoroughly combined.
Arrange the pepper halves cut side up in a 9 by 13-inch baking dish
and fill each pepper half with the meat mixture. Pour the tomatoes over the peppers and sprinkle with the feta cheese
. Cover with foil and bake for 30 minutes. Uncover and bake until the meat mixture is completely cooked and the peppers are tender, about 25 minutes longer.