Pour boiling water over beef; let stand 1 minute; drain.
In saucepan, melt butter; add beef; cook, stirring, until edges curl.
Stir in flour; slowly stir in milk; cook, stirring constantly, until smooth and thickened; add meat sauce.
Peel, slice avocado into lengthwise slices.
On platter, arrange toast; top with creamed beef; arrange avocado slices on top.