Preheat the oven to 350 degrees Fahrenheit.

Heat the avocado oil in a thick-bottomed pot or skillet over medium-high heat and add the chopped onion. Sauté, stirring occasionally, until onion is translucent, about 5 to 8 minutes. Stir in the garlic and sauté for another 2 minutes.

Add the coconut milk, chicken broth, vinegar, sun-dried tomatoes, kalamata olives, Italian seasoning and sea salt and bring the mixture to a full boil. Transfer the baby spinach to the pot (or skillet) and cover it for 1 to 3 minutes to allow it to wilt before stirring it into the sauce. 

Add the tapioca flour (or gluten-free flour) and whisk the sauce well until the clumps of flour are out. Continue cooking the sauce at a boil, stirring frequently, until it has thickened substantially, about 5 to 10 minutes total. Taste the sauce for flavor and add more sea salt and/or vinegar to taste.

Transfer the chicken breasts to a large casserole dish and sprinkle them lightly with sea salt.

Pour the sun-dried tomato sauce over the chicken breasts and give everything a little stir until the breasts are well-coated in sauce.

Bake for 30 to 40 minutes, or until the chicken reaches an internal temperature of 165 degrees Fahrenheit.

Serve the chicken with your choice of side dishes. Steamed rice or noodles are amazing to soak up the sauce! Cauliflower rice and roasted or sautéed vegetables are great options as well.