HEAT 2 TABLESPOONS OLIVE OIL in a skillet over medium heat and add shrimp and scallops. Cover and cook until shrimp and scallops are cooked, about 4 minutes. Remove shrimp and scallops and place in the refrigerator to chill. Add clams, mussels, white wine, vinegar, onion and garlic to pan; cover. Increase heat to high and cook until the shells open, about 5 minutes. Remove from heat. Remove shellfish and add them to the shrimp and scallops in the refrigerator to chill.
Transfer the rest of the contents of the pan to a food processor or blender. Add the cucumber, Tabasco, garlic and 1 cup tomato juice and blend until smooth. Add the mayonnaise, blend until incorporated and taste for salt and pepper.
Pour the mixture into a bowl, add remaining juice and place in the refrigerator to chill. Roast the peppers, remove the skin and seeds and place in the refrigerator to chill. Brush the rounds of bread with remaining olive oil, toast them under a broiler and set aside to cool. When it's time for dinner, arrange 2 shrimp and 2 scallops in a pepper half and place in soup bowls. Spoon some gazpacho around the peppers and arrange the clams and mussels in the soup. Place the croutons on the peppers. Serve well-chilled.