Preheat oven to 350.
Cut a very thin slice off the bottom of each tomato, just enough to see that it sits upright in the dish. Cut a circle around the stem, and remove stem. Scoop out pulp and seeds, leaving a hollow tomato. Place in casserole dish and repeat with remaining tomatoes.
Combine crab, bell pepper, green onions, breadcrumbs, vinegar, Old Bay®, yogurt, and mozzarella in a medium bowl. Stir well. Stuff mixture into tomatoes.
Bake at 350, uncovered, 12-15 minutes or until cheese is melted.