An inspired and inexpensive seafood hors d'oeuvre. salt and freshly ground pepper to taste Combine tuna, butter, lemon juice and Tabasco in a food processor or blender, process until mixture is smooth. Transfer to a bowl, add shrimp, pimiento and capers, mix well. Season with salt and pepper, taste and adjust seasoning (pate must be highly seasoned). Pack into a well-oiled 3-cup loaf pan or mold, chill 24 hours. To serve, let stand 30 minutes at room temperature, unmold on a plate. Garnish with parsley or watercress sprigs and sliced stuffed olives. Serve with buttered toast rounds. *Do not substitute water-packed tuna 10 servings