Preheat the oven to 350.
Grease a 13x9 pan.
Mix the Bisquick and water until a soft dough forms, beat well.
Using floured hands, press the dough into the prepared pan.
Cook and stir the sausage in a skillet until browned, ensuring that there are no large pieces, drain; set aside to cool.
Once the sausage has cooled, mix the sausage, the onions and the mayonnaise or the dressing together in a mixing bowl.
Remove the stems from the mushrooms. Finely chop them; stir them into the sausage mixture.
Fill the mushroom caps with the sausage mixture. Place the mushrooms in rows on the dough in the pan. Sprinkle the cheese and the paprika on top of the stuffed mushrooms.
Cover the pan, loosely, with aluminum foil.
Bake for 20 minutes, then remove the foil.
Bake for an additional 5-10 minutes or until the cheese is bubbly.
Let them stand 15 minutes before serving.