Heat a Dutch oven or large soup pot over medium-high heat. Melt butter in pan then add carrots, mushrooms, celery, and shallots/onions. Saute until the mushrooms release their liquid and the liquid has evaporated, 3-4 minutes.
Season with homemade seasoning salt and pepper then continue to saute, turning the heat down slightly if necessary, until vegetables are tender, another 6-7 minutes.
Add garlic, poultry seasoning, and dried thyme then saute until garlic is very fragrant, 1-2 minutes.
Sprinkle flour over vegetables then stir to coat and cook for 1 minute.
Slowly pour in chicken broth while stirring to avoid lumps then add milk and turn heat up to medium-high.
Bring mixture to a simmer, stirring occasionally, then add gnocchi and stir to combine.
Turn heat down to medium then simmer, stirring frequently, until gnocchi are tender, 5-6 minutes.
Stir in chicken and peas then taste and add seasoned salt and/or pepper if necessary.
Ladle into bowls then serve.
