To smash the Brussels Sprout, you need to microwave them.
In a large microwave-safe dish, place the uncooked Brussels sprouts add ¼ cup of water, and cook for 4 minutes at high temperature.
Remove for the microwave and let them cool for 5 to 10 minutes
Place the Brussels Sprouts on a cutting board, and with the back of a small bowl, smash the Brussels. (You can also use the back of a large spoon, fork, meat mallet, or bottom of a glass.)
Place the smashed Brussels sprouts in a large bowl, add olive oil, balsamic vinegar, grated parmesan, salt, and pepper. Mix gently until the Brussels sprouts are well coated.