1.Melt 1/4 Of The 3 Tablespoon Of Butter In A Skillet Over Medium-High Heat, Add A Mushroom Cap, And Cook On Both Sides Until Completely Soft To The Center, About 3 Minutes. Repeat With Remaining Butter And Mushrooms, And Place The Cooked Mushrooms Upside-Down On An Aluminum Foil-Lined Baking Sheet; Sprinkle With Garlic Powder. 2.Preheat The Oven'S Broiler And Set The Oven Rack At About 6 Inches From The Heat Source. 3.Melt The Remaining 1 Tablespoon Of Butter In A Skillet Over Medium-High Heat. Add The Scallops, And Cook Until Just Firm, And Lightly Browned On Both Sides. Divide Scallops Among Mushroom Caps. Stir Together Mayonnaise And Chili Sauce In A Small Bowl, And Spoon Over The Scallops. 4.Broil Until The Mayonnaise Has Developed Brown Patches And Is Hot, 3 To 5 Minutes. Sprinkle With Green Onions To Serve.