Start by rinsing your mussels and clams under cold water to remove any sand or debris. Peel and devein the shrimp if not done already.

In a large pot, heat the olive oil over medium heat. Add minced garlic and chopped onion, sautéing until fragrant and the onion turns translucent, about 2-3 minutes.

Pour in 6 cups of water and stir in the Cajun seasoning. Adjust the salt as needed and let it come to a gentle boil.

Once your broth is bubbling, add the mussels and clams first, cooking for about 3-4 minutes. Then, add the shrimp and let everything simmer for another 5-7 minutes, or until the shrimp are pink and fully cooked, and the mussels are opened.

Squeeze fresh lemon juice over the seafood, stir well, and remove from heat. Serve the seafood boil hot in a large bowl, garnished with fresh parsley and lemon wedges.