This recipe is adapted from Pamela Salzman's new cookbook Kitchen Matters. I served my tacos with some organic corn tortillas, quick pickled shallots and avocado on the side (see note).
If you don’t mind one more step, doing a quick pickle on the shallots is a delicious way to upgrade them, especially if you don’t like the flavor of raw onion. Toss them with 1 tablespoon cider vinegar, 1 teaspoon honey, and 1/2 teaspoon salt and let them sit for 10 minutes while the mushrooms are cooking. You can also make up to 2 weeks in advance.