Put oven rack in middle position and preheat oven to 400°F. Line a small baking pan with foil. Roast tomato in pan until tender and skin peels off easily, about 30 minutes. While tomato is roasting, slit chile open lengthwise and discard stem and seeds, then tear chile into small pieces. Heat oil in an 8- to 10-inch heavy skillet over moderate heat until hot but not smoking, then add chile and cook, stirring, until fragrant and chile turns a brighter red, 30 seconds to 1 minute. Transfer chile with a slotted spoon to a heatproof bowl. Add hazelnuts to skillet along with almonds, bread, garlic, and red pepper flakes and cook, stirring, until bread and garlic are golden, 2 to 3 minutes. Add mixture (including oil) to chile in bowl and cool slightly. Peel tomato, then coarsely chop and transfer (with juices) to a food processor. Add bread and chile mixture, pimientos, water, vinegar, and 1/4 teaspoon salt and puree until smooth. Thin with water if desired and season with salt.