Season the chicken: Pat the chicken dry.
Sprinkle with salt, pepper, paprika, and onion powder on both sides. This helps lock in flavor and keeps the chicken juicy.
Layer the crockpot: Add the minced garlic to the bottom of the slow cooker. Place the seasoned chicken on top in an even layer.
Add the sauce base: Scatter the butter chunks over the chicken.
Pour in the chicken broth. Stir the Dijon and Italian seasoning into the broth around the sides so it mixes in as it cooks.
Cook low and slow: Cover and cook on Low for 4 to 5 hours (thighs) or 3.5 to 4 hours (breasts), until the chicken is tender and reaches 165°F internally. Avoid lifting the lid too often.
Finish the sauce: Stir in the lemon juice and Parmesan (if using).
Taste and adjust salt and pepper. The sauce should be buttery, garlicky, and bright from the lemon.
Serve: Spoon the garlic butter sauce over the chicken. Top with fresh parsley.
Pair with mashed potatoes, rice, noodles, or roasted vegetables.