Heat oven to 350°. Grease oblong pan, 13x9x2 inches. Mix baking mix and water until soft dough forms; beat vigorously 20 strokes. Press dough in bottom of pan with floured hands. Cook and stir sausage in skillet until brown; drain. Mix sausage, onions and mayonnaise. Remove stems from mushrooms. Finely chop stems; stir into sausage mixture. Fill mushroom caps with sausage mixture. Place mushrooms in rows on dough in pan; sprinkle with cheese and paprika. Cover pan loosely with aluminum foil. Bake 20 minutes; remove foil. Bake until cheese is bubbly, 5 to 10 minutes. Let stand 15 minutes; cut into pieces. 35 appetizers. APPET 33