Pat the turkey breast completely dry with paper towels to ensure the seasonings stick and the skin crisps later.
In a small bowl, mix the olive oil, garlic powder, onion powder, paprika, thyme, salt, and pepper to create a paste.
Rub the spice paste evenly all over the turkey breast, getting under the skin where possible.
Place the quartered onion, smashed garlic cloves, and chicken broth into the bottom of the slow cooker.
Place the seasoned turkey breast on top of the onions and garlic (this acts as a roasting rack).
Cover and cook on LOW for 5-6 hours or HIGH for 3-4 hours, until the internal temperature reaches 165°F at the thickest part.
Preheat your oven's broiler.
Carefully transfer the turkey breast from the slow cooker to a foil-lined baking sheet.
Broil for 3-5 minutes, watching closely, until the skin is golden brown and crispy.
Remove from the oven and let the turkey rest for 10-15 minutes before carving.