Cook spinach according to package EXCEPT omit salt. Drain well, pressing out excess water. Combine eggs, mushroom soup, flour, horseradish and mustard; stir in drained spinach.

Spread hash in baked pastry shell; spoon spinach mixture over. Bake, uncovered for 45 minutes. Combine cheese and pimento; sprinkle over pie. Bake additional 2-3 minutes. Let stand before serving.