Lightly butter one side of each bread slice.
In a large skillet, cook the bread, buttered side down, until browned.
To assemble, place 1 slice of bread, buttered side down, on a microwave-safe plate. Top with ham, pizza sauce, pepperoni, and mushrooms, then cheese. Top with remaining slice of bread, browned side up.
Microcook on 100 percent power (high) about 2 minutes or until cheese melts. (Or melt the cheese under the broiler.) Makes 1 sandwich.