Place fish in a shallow glass dish or pie plate. Pour lime juice over fish to cover completely. Cover and refrigerate at least 1 hour for soft-textured fish or 4 hours if you prefer your fish more firm. (The lime juice will "cook" the fish.)
Combine tomatoes, oil, onion, cilantro and salt; mix well. Let stand at room temperature 30 minutes for flavors to develop.
Drain fish, reserving lime juice. Combine catsup and hot sauce; stir in 2 tablespoons of the reserved lime juice (or more to taste). Spoon this mixture into the bottom of 6 wine goblets, ice cream sundae glasses or large martini glasses.
Spoon half of the tomato mixture over catsup mixture; top with the drained fish. Combine remaining tomato mixture and avocado; spoon over fish. Garnish with lime slices and serve with crackers.Makes 6 Source: