Place the maitakes to a big nonstick skillet, cast iron if you have one. Sprinkle the top with 1 teaspoon taco seasoning. Turn the heat to medium. Place another heavy skillet or pot on top of maitakes to press it down. Put something in the pot to keep it steady and even.
The maitakes will start to cook down, release their juices and flatten out. Listen for the sizzle and check them in a few minutes. At some point, the bottoms will be blackened. Use tongs to flip them over, season, and then char the other side.
Simply slice them up and build your taco!