Coat chicken breasts with lemon juice, then season with salt and pepper. Place chicken breast in a casserole dish and cover with foil. Bake for 20 minutes, or until chicken breasts reach 165 degrees Fahrenheit internal temperature.
Remove chicken breasts from oven and rest 5-10 minutes before slicing. Slice chicken breasts into smaller pieces for easy reheating, then divide between meal prep containers.
In a small saucepan over low heat, combine butter, lemon juice, and garlic. Stir until the mixture is fully melted and combined. Pour over sliced chicken or divide between dressing containers.
Place 1/4 cup of broccoli mash and 1 hardboiled egg in each meal prep container. Allow chicken and sauce to cool for at least 30 minutes before placing lid and refrigerating containers. Refrigerate until ready to reheat, for up to 5 to 6 days.