In a large pot, combine the garlic cloves with the coriander and fennel seeds, crushed red pepper, salt and water. Using a vegetable peeler, remove the zest from the lemon and add to the pot. Halve the lemon, squeeze it into the pot and add the halves. Bring the liquid to a boil and then simmer over low heat for 15 minutes. Add the shrimp and scallops and simmer just until white throughout, about 5 minutes. Drain the shrimp and scallops well and transfer them to a large plate. Leave the aromatics on the seafood. Cover and refrigerate the seafood until chilled, at least 4 hours or overnight.