In a small blender add the lemon juice, olive oil, Dijon mustard, and garlic. Pulse a few times until the dressing emulsifies into a light, pale yellow and the garlic is fully processed. Transfer to a bowl and toss in the herbs. Cover and place in the fridge for 10 minutes.
Prep and clean the seafood: de-shell, de-vein, and remove tails from the shrimp. Rinse the squid and remove any cartilage + cut tubes into 1/4 inch rings. Rinse the scallops.
In a heavy pot of water, add a quartered lemon, a few teaspoons of peppercorns, and a heaping pinch of salt. Bring to a boil, then reduce the heat to a simmer.
On the side, prepare a large bowl of ice water big enough to hold all the seafood.
Cook each seafood separately (ending with the squid):Shrimp ( 1 1/2 to 2 minutes), Scallops (2 1/2 to 3 minutes), Squid Tubes (1 1/2 to 2 minutes), Squid Tentacles (2 to 2 1/2 minutes)
When each seafood is done, fish out of the pot and place in the ice water to blanch and stop cooking.
If enjoying right away, drain, and add to a bowl. Drizzle on the desired amount of dressing and toss to coat. If eating later, drain, and add to an airtight container and refrigerate until ready to dress and serve.