I just went to a Pampered Chef party yesterday and we made the dessert you were looking for. I wouldn't call it Tiramisu but it's a modified version I guess. Here it is.

TIRAMISU BROWNIE SQUARES

1 pkg (19-21 oz) brownie mix (plus ingredients to make cake-like brownies)
1 cup milk
1/4 cup instant coffee granules
1 container (12 oz) frozen whipped topping, thawed, divided
2 pkgs (3.4 oz each) cheesecake instant pudding and pie filling
20 chocolate crème-filled sandwich cookies, coarsely chopped (2 cups, oreos)
2 tbsp semi-sweet chocolate morsels, grated
1/4 tsp korintje cinnamon

Preheat oven to 350 degrees F. Lightly spray Rectangular Baker (13x9-inch baking pan) with nonstick cooking spray.

Prepare brownie mix according to package directions for cake-like brownies; pour batter into prepared pan, spreading evenly.

Bake 25-30 minutes or until cake tester inserted in center comes out clean. Remove from oven; cool completely.

In Batter Bowl (mixing bowl), combine milk and instant coffee granules; stir until dissolved.

Add half of the whipped topping and all fo the pudding mix; whisk until smooth.

Coarsely chop cookies using food chopper; fold into pudding mixture. Spread filling evenly over brownie layer.

Attach open star tip to Easy Accent Decorator (decorating tube); fill with remaining whipped topping. Pipe whipped topping in diagonal rows, 1/4-inch apart, over filling (or drop by spoonfuls).

Grate chocolate morsels over whipped topping using deluxe cheese grater. Sprinkle with cinnamon. Refrigerate at least 30 minutes. Cut into squares.

Yield: 20 servings
Adapted from source