Add garlic, peanut butter, broth, chicken, zucchini, soy sauce, sugar, and red pepper to slow cooker. Stir to combine. Cook on low for 4-5 hours or on high for 2-3 hours. A half hour before you are going to serve, add in lime juice and 1/2 cup of cilantro if desired. Chop chicken into bite size pieces. Serve over noodles & garnish with peanuts and cilantro if desired.