1. Preheat broiler to high.
2. Cut bell peppers in half lengthwise; discard seeds and membranes. Place pepper halves, skin sides up, on a foil-lined baking sheet; flatten with hand. Broil for 13 minutes or until blackened. Place in a paper bag, and fold tightly to seal. Let stand for 20 minutes. Peel and cut bell peppers into 1/2-inch-thick strips.
3. Preheat oven to 450°.
4. Leave root and 1-inch stem on beets; scrub with a brush. Place beets in an 11 x 7-inch ceramic or glass baking dish. Add 1 inch of water to dish; cover tightly with foil. Bake at 450° for 1 hour or until tender. Cool; peel and cut into 1/2-inch-thick slices.
5. Combine olive oil and the next 6 ingredients (through black pepper) in a small bowl, stirring well with a whisk. Place sliced beets in a medium bowl. Drizzle beets with 3 tablespoons vinaigrette; toss gently. Let stand at least 15 minutes. Divide beets evenly among 6 salad plates, and top each serving evenly with peppers, plums, and tomatoes. Drizzle with remaining vinaigrette. Sprinkle evenly with cheese.