Put a dash of olive oil in a pan and let it heat up over medium-high heat.
Add a portion of the sliced mushrooms, so that they are not on top of each other. This way the mushrooms will be crispier and have less water.
Let them cook, stirring occasionally, until they are browned.
Add a pinch of salt and cook for a few more seconds.
Set aside and repeat the process with the remaining mushrooms.
Put a dash of olive oil back in the pan and when hot add the onion and let it brown.
Add the spinach and cook for 1 min.
Add the seasonings, stir well, and set aside along with the mushrooms.
Place 1 tortilla in the frying pan, spread with the vegan cheese and on one half place the mushroom and spinach mixture.
Sprinkle with coriander.
Fold the tortilla in half and let it brown on one side.
Turn the quesadilla over and let it brown on the opposite side.
Repeat the process with all the quesadillas.
Cut the quesadillas into 3 pieces and serve.