Heat a large skillet over medium-high heat. Add the bacon and cook until the fat has rendered and the bacon is browned. Add the garlic and cook just until fragrant, about 30 seconds. Add the mustard greens and stir to wilt. Season with salt and pepper. Stir in the chicken broth and bring to a simmer. Cover and let cook until the greens are tender, about 10 minutes. Stir in the lemon juice and serve immediately.