Take a bowl. Add the Oreo Cookies and crush them until they turn into crumbs.
In a saucepan, add the water, sugar and lemon zest. Whisk well. Add the agar-agar and whisk again. Divide this jelly mixture into three parts.
Take a baking tin. Layout the Oreo Cookies to form the base. Pour one part of the jelly mixture on top and refrigerate for 20 minutes.
Take a saucepan, add the second part of the jelly mixture and the condensed milk. Whisk well. Add ½ cup of crushed Oreos, and fold gently.
Take out the cake tin, pour the condensed milk mixture on top and refrigerate for 20 minutes.
Take the remaining jelly mixture and add ½ cup of chocolate sauce to it. Whisk well.
Pour the prepared chocolate mixture on the cake and refrigerate for 35 minutes.
Once done, dust with cocoa powder.
Pipe whipped cream swirls on the edges of the cake, and place one Oreo Cookie in each swirl. Take a slice, drizzle chocolate sauce and enjoy your Oreo Jelly!