* Planting lettuce: This is the original phrase, referring to the act of putting lettuce seeds or seedlings into the ground.
* Planted lettuce: This refers to lettuce that has been planted and is growing.
* Plantain lettuce: This refers to a type of lettuce that is sometimes used in salads.
* Planting letup: This is a bit of a stretch, but "letup" means a temporary pause or decrease in activity. You could use it in a humorous context to describe someone who is not very enthusiastic about planting lettuce.
There aren't many perfect homophones for "planting lettuce" since it's a relatively specific phrase. However, I hope this list gives you some ideas for wordplay!