This a very yummy and refreshing appetizer! I have made it for team luncheons at work for some of my vegetarian friends. Also when some friends have given up meat for lent, this has been something I have brought in that they love. I have served at many parties and brunches.
Heat oven to 375 degrees. Separate dough into 4 long rectangles. Place rectangles crosswise in un-greased 15 x 10 jelly roll pan or big cookie sheet works too. Press over bottom and 1 inch up sides to form a crust (you don't have to do that I have done it both ways and I choose not to do a crust since I use this as an appetizer). Seal perforations. Bake for 14 to 19 minutes or until golden brown. Cool Completely.
In a small bowl, combine sour cream, horseradish, salt and pepper and blend till smooth. Spread evenly over cooled crust. Top with mushrooms, tomatoes, broccoli, green pepper and onions.
Cut into appetizer size pieces. Refrigerate leftovers. Can make a lot of appetizers depending on the size you cut them (pizza cutter works good).