1. Heat a Dutch oven over medium-high heat. Add pork to pan; cook 2 minutes. Add onion and fennel to pan; cover and cook 15 minutes, stirring frequently. Add salt and next 4 ingredients (through pepper); cook 1 minute, stirring constantly. Add tomatoes and 1/4 cup vinegar to pan. Reduce heat to medium. Uncover and cook an additional 15 minutes or until pork is tender, stirring frequently.
2. Combine olive oil and 2 teaspoons vinegar in a medium bowl. Add green and red cabbage; toss gently to coat.
3. Combine yogurt, mayonnaise, and garlic in a small bowl. Spread about 1 1/2 teaspoons yogurt mixture onto each bun half. Top bottom half of each bun with 1/4 cup fennel mixture, 1/4 cup cabbage mixture, and top half of bun.