Rinse and drain lentils. Place in medium heavy saucepan and add onion halves (with cloves), bay leaf, and enough water to cover by an inch. Bring to the boil, reduce to barely a simmer, cover and cook 20 minutes. Add salt and pepper, and a little more water if none is visible when you tilt the pan, and cook another 1020 minutes until lentils are creamy inside but still intact. Drain and remove onions and bay leaf. Let cool.
Mix lentils in a bowl with fennel, radishes, green pepper, carrot, onion and garlic. Make vinaigrette by whisking together vinegar and mustard in small bowl, then gradually drizzling in olive oil while whisking until and emulsion is formed. Pour vinaigrette over lentils and vegetables, add oregano, and stir well. Taste and adjust seasoning if necessary. Serve at room temperature.
c.1997, M.S. Milliken & S. Feniger, all rights reserved