Rinse and sort the yellow split peas under cold water, removing any debris.
Add the rinsed yellow split peas, diced onion, diced carrots, diced celery, and minced garlic to the slow cooker.
Pour in the vegetable broth and stir to combine all ingredients.
Add the dried thyme, ground cumin, smoked paprika, black pepper, salt, olive oil, and bay leaf to the slow cooker. Stir gently to mix the seasonings evenly.
Cover the slow cooker with its lid and cook on low for 6 hours.
After cooking, remove the bay leaf from the soup.
Use an immersion blender to puree the soup slightly, leaving some texture, or transfer half the soup to a blender, blend until smooth, and return it to the slow cooker. Stir well.
Taste and adjust seasoning with additional salt or pepper if needed.
Ladle the soup into bowls and garnish each serving with chopped fresh parsley.
Serve hot and enjoy your slow cooker yellow split pea soup.