Warm a large skillet over medium heat. Add ground turkey and cook for 4–5 minutes, stirring occasionally, until it starts to brown slightly.
Transfer the partially cooked turkey into the slow cooker.
Add Brussels sprouts, olive oil, garlic, salt, and pepper to the slow cooker. Stir gently to combine.
Cover and cook on low for about 5 hours or high for 2½–3 hours, until the Brussels sprouts are tender and the turkey is fully cooked.
Check near the end of cooking. If the mixture looks dry, stir in a splash of broth or water.
Optional: add smoked paprika, balsamic vinegar, or a squeeze of lemon juice before serving for extra flavor.
Serve warm as is, or spoon over rice, quinoa, or mashed potatoes. Store leftovers in the fridge or freeze for later use.