Heat oven to 350°F. In medium bowl, combine roast beef, taco sauce, barbecue sauce, onions, 1/4 cup olives and cheese; mix well. Set aside.
Separate dough into 10 biscuits. Dip both sides of each biscuit in cornmeal. Press or roll each biscuit to form 5-inch round. Place 5 rounds on ungreased cookie sheet. Spoon about 1/4 cup of roast beef mixture onto center of each round. Brush edges lightly with water. Place remaining 5 biscuit rounds over roast beef mixture. Press edges with fork to seal. With back of tablespoon, make indentation in center of each sandwich; sprinkle with remaining cornmeal.
Bake at 350°F. for 14 to 22 minutes or until golden brown. Remove from oven; if necessary, gently repeat indentation. Fill each with 1 heaping tablespoon sour cream. Garnish each with 2 pimiento slices and 2 olive slices.