1. Heat oil in a large skillet over medium heat. Add onion to pan; cook 10 minutes or until golden, stirring occasionally. Add apple; cook 1 minute. Add cabbage and next 3 ingredients (through caraway); cover and cook 10 minutes or until cabbage is crisp-tender, stirring occasionally. Uncover and add 1/4 teaspoon salt; cook 6 minutes or until liquid evaporates. Remove from heat; stir in parsley.
2. Combine yogurt and next 10 ingredients (through red pepper) in a small bowl; stir well with a whisk.
3. Divide roast beef evenly among rye toasts; top each serving with 2/3 cup slaw. Drizzle about 1 tablespoon dressing over cabbage.