Combine the ground turkey, almond flour, egg, minced garlic, oregano, salt, and black pepper in a mixing bowl. Mix gently until just combined.
Shape the mixture into 16 meatballs of roughly equal size and set them aside on a plate.
Pour the crushed tomatoes into the slow cooker. Stir in the Italian seasoning and half of the chopped basil.
Add the meatballs to the sauce in a single layer. Scatter the zucchini slices over and around the meatballs.
Cover and cook on low for 6 hours or until the meatballs reach an internal temperature of 165°F.
Stir in the remaining basil just before serving.