Drizzle avocado oil in the bottom of the slow cooker. Add the chicken breasts and season with garlic powder, onion, powder, parsley, oregano, and paprika.
In a medium saucepot, melt the butter over medium heat, then whisk in the flour. Cook the roux for 1-2 minutes. Whisk the cornstarch with the chicken stock, then whisk it into the roux. Simmer, whisking constantly until the gravy has thickened to your liking.
Pour the gravy into the slow cooker and cover. Cook on low for 4-5 hours or until the chicken is fall-apart tender.
Serve on egg noodles or rice, with a sprinkling of parsley.I like to serve this chicken and gravy with a side of peas for an English-inspired dinner.