Mix the ingredients in a bowl. You don't need to worry about the lumps so much.
Wash the mizuna leaves, cut into 2 cm lengths, and drain the excess water. Cut the wiener sausages into small pieces, and drain the excess water from the corn.
Add the Step 2 ingredients and cheese into the Step 1 bowl, and mix well until the mixture is no longer lumpy. If the batter is too thick, add a little bit of water.
Heat a large amount of oil in a frying pan. After giving the batter another quick mix, pour 1/2 of it into the pan and shallow-fry by pressing it down. When both sides become crispy, it's ready to be served.
Addendum: Since the water content of the ingredients affects the thickness of the batter, I allowed for excess. Please check the consistency of the batter during Step 3, and adjust the amount of water as necessary.