Heat the olive oil in a large skillet over medium-high heat. Add the lamb pieces and brown them on all sides for about 5 minutes.
Add the diced onion and minced garlic to the skillet. Cook for 3 minutes until the onion softens.
Transfer the lamb mixture to the slow cooker. Pour in the diced tomatoes, chicken broth, herbes de Provence, salt, and black pepper.
Stir to combine, then cover and cook on low for 6 hours.
Add the sliced zucchini during the final hour of cooking. Stir gently and continue cooking until the zucchini is tender.
Taste and adjust salt or pepper if needed. Sprinkle with chopped parsley before serving.