In a large pot, bring 4 quarts of water to a boil. Add the Cajun seasoning, salt, lemon halves, onion, and garlic. Stir to combine.
Carefully add the eggs to the boiling water and cook for 10 minutes for hard-boiled eggs. Once done, transfer the eggs to an ice bath to cool for about 5 minutes.
In the same pot, add the smoked sausage, baby potatoes, and corn. Cook for an additional 15-20 minutes, or until the potatoes are tender.
Drain the pot, reserving a little bit of the cooking liquid if desired.
In a large bowl, combine the drained sausage, potatoes, and corn with the melted butter. Peel the cooled eggs and add them to the bowl. Toss everything gently to coat.
Serve immediately, garnished with chopped parsley and additional Cajun seasoning if desired.