In a small bowl, mix all ingredients together until well combined. Cover and place in the refrigerator until ready to use.
For the Seafood Platter:
Divide each crab cakes in half and form each half into a smaller sized cake (should have 12 total). Cook accordingly to package directions.
Using a large platter, put down a layer of lettuce and place a bowl of the mustard sauce in the middle. Arrange the crab cakes, shrimp, lobster, and lemon wedges on top of the lettuce and around the mustard sauce. Serve immediately with the additional accompaniments.
Store leftover mustard sauce, covered, in the refrigerator for up to 1 week.