Prep the mushrooms: Remove the stem from each mushroom. Use a spoon to scrape gills out of the mushrooms. Slice caps into finger-width slices.
Cook the mushrooms: Heat oil in a pan over medium-high heat. Once hot, add sliced mushrooms. Cook for 3-4 minutes, until softened and golden.
Simmer the mushrooms: Add barbecue sauce to the pan. Bring the sauce to a simmer. Add 1-3 tablespoons vegetable broth as needed to thin the sauce enough to cover the mushrooms. Simmer, uncovered, for 4-5 minutes. Stir as needed to avoid burning the sauce. The mushrooms are ready when softened and chewy.
Make the coleslaw: Meanwhile, make the coleslaw by whisking together the mustard, lime juice, apple cider vinegar, hot sauce, and sugar in a large bowl. Add the shredded cabbage. Using tongs, toss the cabbage until it is well combined with the dressing. Cover and refrigerate until ready to use.
Prepare corn tortillas by heating them in an unoiled pan over medium high heat. Flip after they are lightly browned and starting to puff, about one minute.
Serving: Divide the BBQ portobellos evenly between 6 corn tortillas. Add ~½ cup slaw to each tortilla. Top with roasted pumpkin seeds, cilantro, lime zest, and a squeeze of lime juice. Enjoy!
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Notes
Portobello mushrooms: This recipe also works with crimini or white mushrooms. If using these smaller mushrooms, slice them in 2-3 pieces instead of strips.
BBQ sauce: I use ketchup-based homemade vegan BBQ sauce. Vinegar-based and mustard-based sauces also work but will result in much tangier tacos.
Protein: For more protein, serve with canned chickpeas, crispy chickpeas, or baked tofu.
Leftovers: Refrigerate leftover mushroom filling and coleslaw in a closed container for 3-4 days. Reheat in the microwave or on the stove over medium-low.