Place the tofu on a dish and cover with plastic wrap. Microwave for 1 1/2 minutes. Take off the wrap and drain the liquid.
Chop and mash the umeboshi using a knife, and mix with the grated ginger and mentsuyu.
Inset chopsticks into the tofu (don't insert them all the way through) to make a passage for the heat. Remove the chopsticks and top with Step 2.
Cover with cheese and microwave for 1 minute uncovered. Sprinkle with nori (etc.) and you're done!
I tried making this once by skipping Step 1 and just heating the tofu in Step 4...But the tofu was watery and still cold in the middle, so I wouldn't recommend it!
Story Behind this Recipe
This is a variation of another recipe of mine which uses salted dried konbu seaweed and cheese on hot tofu.
It's more delicious if you lightly grill the nori in Step 4 before you sprinkle it on. It was also good when I added wakame to Step 2! You can use soy sauce instead of mentsuyu, but I thought it may be a little too salty. It depends on how sour and salty the umeboshi are and the amount of ginger you add.