Combine turkey broth and chicken bouillon in a slow cooker.
Place bacon in a skillet over medium heat; add garlic and black pepper. Cook and stir until bacon is crispy, about 10 minutes. Transfer to a paper towel-lined plate; blot to remove as much fat as possible.
Stir bacon mixture into the slow cooker. Add turkey, red onion, barley, rosemary, salt, and Italian seasoning.
Cook, stirring every half hour, on Low for 7 1/2 hours (or high for 3 1/2 hours). Stir okra and parsley into soup and continue cooking for 30 minutes more.
Cool soup to room temperature and refrigerate, 8 hours to overnight. Skim any solid fat off the top and heat soup on the stovetop.
