Lay the chicken breasts on the bottom of the slow cooker and drizzle with olive oil. Sprinkle with Italian Seasoning Blend, 1 tsp garlic powder, 1 tsp salt -- do not toss. Leaving the seasonings undisturbed helps to more richly season the chicken breasts as it cooks.
Place the uncooked Italian sausage links atop the seasoned chicken. Do not mix.
Next, place the layer of thinly sliced onion and chopped garlic. Pour the canned diced tomatoes, tomato sauce, chicken stock (or water) and balsamic vinegar into the slow cooker basin. Top with the remaining seasonings (1 tsp Italian Seasoning Blend, 1/2 tsp kosher salt, and 1/2 tsp garlic powder). Again, do not mix. The flavors develop nicely when left in layers as directed.
Cover the slow cooker, set to high temperature and cook for 5 hours.
Shred the chicken breasts in the slow cooker basin and combine with the sauce. Remove the Italian sausage links, slice into coins and mix back into the sauce. Serve with spaghetti squash for Paleo, gluten-free pasta or regular pasta, as desired.