Heat the olive oil in a large Dutch oven over medium heat.
Add the onion, carrots, and celery. Cook for 10–12 minutes, stirring occasionally, until softened and lightly browned.
Add the garlic and cook for 30 seconds until fragrant.
Stir in the split peas, chicken broth, ham hock, bay leaf, thyme, black pepper, and salt.
Bring the soup to a boil.
Reduce the heat to low and partially cover the pot.
Simmer for 90–105 minutes, stirring occasionally, until the split peas are completely tender and the soup is thick and creamy.
Remove the ham hock and bay leaf.
Pull the meat from the ham hock, discard the bone and any tough pieces, then return the meat to the soup. Add the diced ham if using.
Stir in the Worcestershire sauce and lemon juice.
Taste and adjust seasoning with additional salt and pepper if needed.
Add additional broth if a thinner consistency is desired.
Garnish with fresh parsley and serve hot.