3 tablespoons olive oil
1 pound fresh mushrooms like shiitake or oyster, shiitakes stemmed and thinly sliced
Kosher salt and freshly ground black pepper
Pinch of dried red chile flakes
2 skinless fillets cod or other firm white fish like snapper or hake (about 1 pound)
1 cup homemade vegetable stock or low-sodium vegetable broth
2 tablespoons fresh squeezed lemon juice from 1 lemon
Fresh cilantro, parsley or chives, for garnish (optional)