Step 1: Season the chicken — Pat the chicken breasts dry with paper towels. Stir together the Italian seasoning, garlic powder, onion powder, paprika, salt and black pepper, then rub the mixture all over the chicken.
Step 2: Load the slow cooker — Pour the chicken broth into the slow cooker. Arrange the seasoned chicken breasts in a single layer and dot with the butter.
Step 3: Slow cook — Cover and cook on LOW for 3–4 hours or HIGH for 1½–2 hours, matching the time to breast size: small breasts LOW 2½–3 hours / HIGH 1½ hours, medium LOW 3–3½ hours / HIGH 1½–2 hours, large LOW 3½–4 hours / HIGH 2–2½ hours. The chicken is done when the thickest part reaches 165°F (74°C); start checking 30 minutes early.
Step 4: Rest — Transfer the chicken to a plate and rest for 5 minutes.
Step 5: Shred and serve — Shred with two forks or slice across the grain, then drizzle with the cooking juices.
Step 6: Freeze for meal prep — Portion the shredded chicken into freezer bags with some of the broth, label and freeze for up to 3 months.