In a large bowl, whisk together jello, sugar, water, and lemon juice until sugar is dissolved. Cover with plastic wrap and refrigerate until almost set (about 1 hour).

Press crushed lemon oreos into the bottom of a 9×13" pan, set aside.

In a medium bowl, pour chilled evaporated milk. Beat until stiff peaks start to form (about 3-5 minutes). Add whipped evaporated milk to the jello mixture, and fold in until completely combined. Pour mixture over oreo crust.

Freeze for 2-3 hours, until set. Cut into squares and serve topped with lemon slices and lemon zest.