Scrub potatoes well. Place in a large saucepan, and cover with water. Heat to boiling. Reduce heat slightly to a soft rolling boil, and cook 15 minutes. Drain, and allow to cool slightly.
Preheat oven to 425 degrees. Cut potatoes into quarters, and put in a large bowl, along with Brussels sprouts and green beans. Add 1 tablespoon olive oil, tarragon, salt, and pepper. Stir well to coat. Place vegetables on a baking sheet. Bake 10 minutes, and flip. Cook another 10 minutes, or until vegetables are slightly blackened. Place in a large bowl, and set aside.
Heat 1/2 tablespoon olive oil in skillet over medium heat. Add onions and pecans, and cook until onions are soft and translucent. Mix in with potatoes and vegetables. To serve, place ½ cup lettuce on each plate, and top with roasted potato-vegetable mixture. Drizzle a little olive oil over each serving, if desired.
Yield: 4 servings (serving size: about 1 cup)