Prep the chicken: Pat the chicken breasts dry with paper towels.
This helps the seasoning stick and keeps the texture better.
Season generously: In a small bowl, mix salt, pepper, thyme, rosemary, oregano, and paprika. Rub the chicken with olive oil, then coat all sides with the seasoning blend.
Layer in the crockpot: Place the chicken breasts in a single layer in the slow cooker. Sprinkle the minced garlic over the top and scatter the butter pieces around the chicken.
Add liquids: Whisk the chicken broth with lemon juice and Dijon mustard.
Pour around the sides of the chicken, not directly on top, so the seasonings stay put.
Cook low and slow: Cover and cook on Low for 3 to 4 hours, or on High for 1.5 to 2.5 hours. The chicken is done when the internal temperature reaches 165°F (74°C) and it’s tender.
Optional: Thicken the sauce: Transfer the cooked chicken to a plate and tent loosely with foil. Stir the cornstarch and water into a slurry, then whisk it into the crockpot liquid.
Cover and cook on High for 5 to 10 minutes until slightly thickened.
Finish and serve: Return the chicken to the sauce or spoon the sauce over the top. Garnish with fresh parsley. Serve with mashed potatoes, rice, couscous, or roasted vegetables.