1 pound lean ground beef
1 (10-ounce) package frozen chopped spinach, thawed and squeezed dry
1 medium zucchini, coarsely grated (about 2 cups)
1 small onion, minced (about 1 cup)
1/2 cup bulghur
1 egg, lightly beaten
1/2 teaspoon dried oregano
1/2 teaspoon salt
Freshly ground black pepper
3 red bell peppers, halved lengthwise, cores and ribs removed
2 (14 1/2-ounce) cans low-sodium stewed tomatoes, finely chopped
1/3 cup crumbled feta cheese