Prep the chicken. Pat the chicken dry with paper towels. If using large breasts, slice them in half horizontally for even cooking.
Season lightly with salt and pepper.
Mix the sauce. In a bowl or directly in your baking dish, whisk together balsamic vinegar, olive oil, minced garlic, honey, Dijon mustard, soy sauce, Italian seasoning, and a pinch of black pepper.
Dump and coat. Add the chicken to the dish and turn to coat. If you’re in a rush, go straight to cooking. If you have time, marinate for 15–30 minutes for deeper flavor.
Oven method. Preheat oven to 400°F (200°C).
Bake uncovered for 18–22 minutes for breasts or 22–28 minutes for thighs, depending on thickness. Spoon sauce over the chicken halfway through. Cook until the thickest part reaches 165°F (74°C).
Slow cooker method. Add everything to the slow cooker.
Cook on Low for 3–4 hours or High for 2–2.5 hours, until tender and fully cooked.
Optional sear. For extra color, quickly sear the cooked chicken in a hot skillet with a little oil for 1–2 minutes per side, then pour the sauce over to glaze.
Reduce the sauce. If you want a thicker glaze, pour the pan juices into a small saucepan. Simmer for 3–5 minutes until slightly thickened. Taste and adjust with a pinch of salt or a splash of balsamic.
Serve. Slice or serve whole with rice, quinoa, or potatoes.
Spoon the balsamic garlic sauce over the top. Garnish with chopped parsley or basil if you like.