Prep ingredients:
Slice chicken into bite-sized pieces. Cut potatoes and carrots into large chunks; dice onion and celery; mince garlic.Layer in slow cooker:
Place onion, celery, carrots, potatoes, garlic, tomato paste, thyme, bay leaf, salt, and pepper into the slow cooker. Add chicken and pour in broth until ingredients are just covered.Cook until tender:
Cook on Low for 6 to 7 hours or on High for 3 to 4 hours, until chicken is tender and vegetables are soft but not mushy.Finish with peas and thicken:
Fold in peas during the final 15 minutes. To thicken, mix flour or cornstarch with water to make a slurry and stir in, or mash some potatoes directly in the pot. Finish with a knob of butter and chopped parsley.