Combine first 3 ingredients in a 2-quart saucepan; bring to a boil. Cover, reduce heat, and simmer 10 minutes; drain. Discard bay leaf. Return peas to pan; cover and set aside.
Meanwhile, heat oil in a large skillet over medium-high heat. Add onion; cook 5 minutes or until golden, stirring often. Reduce heat; add ham, and cook 10 additional minutes or until ham is crisp and onion is well browned. Stir in vinegar, chopped thyme, and pepper; bring to a boil. Cook, stirring occasionally to loosen any caramelized bits from bottom of pan, 5 minutes or until mixture is a thin syrup. Pour over peas; toss well. Garnish, if desired.