Defrosting lettuce from the freezer is not recommended. Freezing causes ice crystals to form within the lettuce, which damages the cell structure and leads to a mushy, watery texture when thawed. As a result, the lettuce will lose its crispness and fresh taste, making it unappetizing for salads or other dishes where crispness is desired.
If you accidentally froze lettuce and now need to use it, your best option is to cook it rather than trying to restore its original texture. Cooking frozen lettuce can work in certain dishes like soups, stews, or stir-fries, where crispness is not essential.
However, if you're looking to enjoy fresh, crisp lettuce in salads or cold dishes, it's better to avoid freezing it in the first place. If you have excess lettuce, consider using it in salads or other recipes before it starts to wilt. If you anticipate having more lettuce than you can use, you can try donating it or composting it instead of freezing it.