Mix the herbs and garlic together in a small bowl. Flatten the chicken breasts by pressing them gently against the work surface with the palm of your hand. Arrange each breast on a large piece of aluminum foil and season with salt and pepper. Sprinkle the herb and garlic mixture over the chicken breasts.
Arrange 2 lemon slices over each breast. Dot with the butter and seal the packets. Set on a baking sheet.
Set the packets on the center rack of the oven and bake until done, 30 minutes. Transfer to serving plates and allow the guests to open the packets at the table.