Tear kale into pieces, discarding ribs, and put in a bowl or plastic bag. Carefully cut zest from lemon half with a small knife. Cut zest into slivers and add to kale. Dress kale with juice from lemon, oil, and parmesan. Season to taste with salt and pepper.
Cut avocados in half and dice flesh. Spoon out flesh onto both sides of each sandwich roll and smash to spread. Season to taste with salt and pepper. Spoon kale mixture onto one side of each roll and cover with top of roll. Eat right away, or wrap in foil or waxed paper and pack in your backpack for later for a pressed sandwich. (The kale wilts a bit but still tastes great.)
*A tiny plastic container like those made by Nalgene is handy for transporting olive oil, or buy oil packets such as Marconi: Marconi organic olive oil packets each hold a single serving (about 0.375 oz.; $5.50/six-pack; backpackerspantry.com).