Chop one of the chipotle chillies and set aside.
Heat the oil in a frying pan over medium heat. Add the sliced mushrooms and cook, stirring occasionally.
After 5 minutes, add the onion and garlic. Season with salt and oregano.
Cook for about 15 minutes, until the mushrooms reduce in size and become tender. If the mixture becomes too dry, add a splash of water.
Add the chopped chipotle chilli and fresh coriander. Cook for 2 more minutes, then turn off the heat.
Serve warm with tortillas for tacos, or add cheese and make delicious mushroom quesadillas.