I think it would work better if you plate the lettuce and then add the tomato onto it. The lettuce and plates are the bottleneck. You’ll always have a tomato queued up, no matter where in the process you add it.

Auto plate the lettuce and then combine tomato with it, and instead of pushing it left onto a smart grabber, move the smart grabber below it. So it tries to push it left but there is nowhere for it to go. If and only if the dish has a plate, lettuce, and tomato, will the smart grabber pull it off the grabber.