Heat olive oil in a skillet and sauté onions, carrots, and celery until soft.
Add garlic and cook briefly until fragrant.
Transfer vegetables to crockpot along with chicken, lentils, tomatoes, broth, thyme, cumin, bay leaf, salt, and pepper.
Cover and cook on low for 6 to 8 hours or high for 3 to 4 hours until chicken is tender and lentils are soft.
Remove bay leaf, taste, and adjust seasoning as needed.
Serve warm topped with fresh parsley.