Cut carrots and celery into 1/2-inch pieces. Dice onion and mince garlic.
Put onion, carrots, celery and garlic in a 6-quart slow cooker. Add herbs, salt and pepper, then arrange thawed chicken thighs over the vegetables.
Pour in chicken broth and cover.
Cook on low for 5 to 6 hours or high for 2 1/2 to 3 1/2 hours, beginning checks at the earliest time.
Remove each thigh when its thickest center reaches 165°F. Rest 5 minutes, discard bay leaves and shred chicken into bite-size pieces.
Set cooker to high. Stir dried egg noodles into hot broth, cover and cook 15 to 25 minutes, stirring once and checking early.
Return shredded chicken and add frozen peas. Cover 3 to 5 minutes, just until hot.
Switch off cooker, stir in lemon juice and parsley, taste with a noodle and adjust seasoning.
