Following the cleaning method mentioned above, clean the mushrooms. Decide how to cut them. You can slice them, but I prefer cutting them into ½-¾ inch cubes. They'll shrink when cooked, so this keeps them from getting too tiny. Chop the stems last.
Peel and chop the half onion and garlic. Wash and dice the tomatoes. Cut the serrano in half.
Heat the oil in the pan over medium-high heat. When ready, add the onion and sauté for 2-3 minutes until it starts to look translucent and soft.
Add the garlic to the center of the pan, stirring while it becomes golden and changes color, about 30 seconds, then mix with the onion for another 20-30 seconds.
Add the tomatoes, serrano pepper, and salt. Stir to combine. Cook for 3-4 minutes, stirring occasionally, until the tomato softens and reduces.
Add the mushrooms. At first it might seem like too many for your pan, but they'll gradually reduce in size.
Stir until all ingredients are combined. After 1-2 minutes, you'll see the mushrooms start releasing lots of water, creating a flavorful liquid at the bottom, this is where all the flavor concentrates.
Lower to a simmer and cook for about 5 minutes, stirring occasionally, until most of the liquid has reduced and the mushrooms are tender but still juicy.
While they're cooking, chop the cilantro. At the end of cooking, add the cilantro, taste and adjust salt, and turn off the heat. Enjoy!
Course: Vegggies
Cuisine: Mexican
Notes
Pro tip for efficient cutting: Hold the mushroom cap firmly between two fingers as you start cutting. This prevents the first slice from sticking to the knife and helps you work faster.