Preheat oven to 400°.
Combine potato and broth in a saucepan; bring to a boil. Cover, reduce heat, and simmer 12 minutes. Drain potato through a sieve into a bowl, reserving 1 cup cooking liquid.
Heat 2 teaspoons oil in a large nonstick skillet over medium heat. Add onion, bell peppers, salt, and garlic; sauté 2 minutes. Stir in 1/4 cup reserved cooking liquid and paprika; cover and cook 8 minutes or until peppers are tender. Stir in potato, 3/4 cup reserved cooking liquid, vinegar, and tarragon; bring to a boil, stirring to coat. Spoon potato mixture into a 2-quart casserole coated with cooking spray. Combine the breadcrumbs and cheese, and sprinkle over potato mixture. Drizzle breadcrumb mixture with 2 teaspoons oil. Bake at 400° for 25 minutes or until golden brown.