1. In 2-quart saucepan over high heat, heat water to boiling. Add shrimp; heat to boiling. Reduce heat to medium; cook shrimp 1 minute, until shrimp are tender and turn pink; drain and keep warm.
2. In same saucepan, combine white wine, wine vinegar, green onion, and garlic. Over high heat, heat mixture to boiling. Boil about 5 minutes or until liquid is reduced to about 2 tablespoons. Discard green onion and garlic. Reduce heat to medium; add butter, 2 tablespoons at a time, beating constantly with wire whisk until butter is melted and mixture is thickened. Keep butter sauce warm. (Do not use margarine; sauce will not be thick.)
3. To serve, peel and remove seed from avocado; cut avocado into 12 wedges. On each of 6 warm small plates, spoon some butter sauce; arrange 2 avocado wedges and a few shrimp.