1. In a saucepan, cover the black-eyed peas with water and bring to a boil. Simmer over low heat until tender, 45 minutes. Drain.
2. Meanwhile, in a skillet, heat the oil. Add the onion, season with salt and cook over moderate heat, stirring, until softened. Cover and cook, stirring occasionally, until browned, 8 minutes. Transfer to a bowl.
3. Roast the bell pepper directly over a gas flame or under the broiler, turning, until charred. Let cool. Peel and seed the bell pepper; cut into 1/4-inch dice.
4. In a saucepan of boiling salted water, cook the diced celery for 30 seconds. Drain, rinse under cold water and drain again.
5. Add the mayonnaise and vinegar to the onion. Fold in the black-eyed peas, bell pepper, celery and scallions; season with salt, pepper and Tabasco. Chill before serving.