Preheat the oven to 425°F (220°C).
In a large bowl, toss the cauliflower florets with 2 tablespoons of the olive oil until evenly coated. Sprinkle with the chili powder, paprika, coriander, cumin, red pepper flakes, and a generous pinch of salt. Toss again until the cauliflower is evenly coated. Spread the cauliflower on a rimmed baking sheet. Bake for 20 minutes, until crispy.
Heat the remaining 2 tablespoons of olive oil in a large skillet over medium heat. Add the onion, poblano, and red bell pepper and sauté until the onion is tender and a bit golden, about 15 minutes. Add the garlic and sauté for another minute. Stir in the mushrooms, then season with salt and pepper. Cook until the mushrooms are tender and crispy (5 to 8 minutes). Remove from the heat and stir in the lime juice. Taste and adjust the seasonings as desired.
For each taco, put 1/4 cup (60ml) of the mushroom mixture in a tortilla. Top with some of the roasted cauliflower and a tablespoonful of cilantro.
Reprinted with permission from _Food52 Vegan_, by Gena Hamshaw, copyright © 2015, published by Ten Speed Press, an imprint of Penguin Random House LLC. Photographs copyright © 2015 by James Ransom.