Heat a griddle (or use a sandwich press) or cast-iron skillet to very hot. Spread the mustard and sour cream on the top halves. On the bottom halves layer the roasted pepper, mushrooms, spinach, olives, cheese and pickle. Cover with the top halves, and wrap each sandwich tightly in aluminum foil. Place these sandwiches on the griddle or skillet, and then place a heavy skillet on top; try to distribute the weight evenly over the sandwiches. (You can even use a brick to do this!) Cook 3 to 5 minutes, pressing down occasionally to flatten the sandwiches. Serve immediately.
Recipe courtesy of Rafael Palomiro, Sonora Restaurant, New York, NY