Mix together onion, peppers, tomatoes, garlic, vinegar and zest. Let sit in the fridge for at least an hour to allow the flavours to meld. Season to taste with salt & pepper. Scrub and rinse oysters well, and shuck. Rinse the meat and inside of the shell under cold running water to remove any debris, and sit them on crushed ice in their lower shell. Spoon about 1/2 tsp of the salsa onto the meat of each oyster. Top with 3 or 4 shakes of Tabasco sauce. Serve immediately. Makes 2-4 servings.