Heat oven to 400°F. Cut bell peppers in half lengthwise; remove seeds and membranes, but not stem. Place peppers, cut-sides up, on two rimmed baking sheets.
Combine ground beef, vegetable juice, spinach, couscous, garlic, oregano, salt and black pepper in large bowl, mixing lightly but thoroughly. Spoon beef mixture evenly into peppers. Sprinkle with cheese.
Bake, uncovered, 25 to 30 minutes or until instant-read thermometer inserted into center of pepper registers 160°F and peppers begin to brown. Let stand 5 minutes before serving.