Avocado Salad with Peaches

1/2 red bell pepper, cored and seeded 2 tablespoons red wine vinegar 1/2 vanilla bean, seeds scraped 1/2 teaspoon sugar 1/4 cup extra-virgin olive oil 2 almost-ripe avocados 8 cups arugula or sorrel 2 peaches, diced and peeled   Preparation Roast bell pepper. Peel and...