Preheat oven to 400 degrees. In a large saucepan, bring 6 cups of water to a boil. Add beans; cover and cook for 3 minutes. Drain and immediately place the beans in ice water. Drain and pat dry. Set aside.
NOTE: I skipped this step and found that the green beans were well cooked just from roasting in the oven. If you prefer a more tender bean, you may want to blanche them as described above.
Remove the papery outer skin from the garlic head (do not peel or seperate the cloves). Cut off top of garlic bulb. Place cut side up on a baking pan and drizzle with olive oil. Add potatoes and drizzle with 2 Tbsp. oil and some salt and pepper. Toss to coat. Bake uncovered at 400 degrees for about 30-40 minutes until the garlic is softened.
Remove the garlic and set aside. Add to the baking pan the red peppers, onions and green beans. Toss to coat with oil. Bake 20-30 minutes longer until veggies are tender. Cool for 10-15 minutes.
Squeeze the softened garlic into a bowl and mash with a fork. Then stir in vinegar, oil, honey, rosemary, and salt. Add to the vegetables; toss to coat. Serve warm or cold.