Layer the chicken thighs, sliced mushrooms, and diced onions at the bottom of the slow cooker. Season generously with salt, pepper, and minced garlic.
In a medium bowl, whisk together the chicken broth, white wine (or extra broth), Worcestershire sauce, and Dijon mustard. Pour this mixture over the chicken and vegetables, ensuring everything is well coated.
Cover the slow cooker and cook on high for 3-4 hours, or on low for 4-6 hours, until the chicken is tender and cooked through.
