Load the crockpot: Add onion, carrots, celery, potatoes, garlic, thyme, parsley, rosemary, bay leaf, salt, and pepper.
Place chicken on top. Pour in chicken broth.
Cook: Cover and cook on Low for 6–7 hours or on High for 3–4 hours, until the chicken is fork-tender and the vegetables are soft.
Shred the chicken: Transfer the chicken to a cutting board and shred with two forks. Remove the bay leaf.
Return shredded chicken to the crockpot.
Make the roux: In a small saucepan, melt butter over medium heat. Whisk in flour and cook 1–2 minutes until it smells nutty. Slowly whisk in half-and-half until smooth and thickened, 3–5 minutes.
Combine and thicken: Stir the roux mixture into the crockpot.
Add Worcestershire and lemon juice. Mix well. Cook on High for 20–30 minutes until the filling is creamy and coats a spoon.
Finish with veggies: Stir in frozen peas and corn.
Cook 5–10 minutes more, just until heated through. Taste and adjust salt and pepper.
Serve: Spoon the filling into bowls and top with warm biscuits or puff pastry. Garnish with parsley if you like.