What these veggie tacos lack in meat, they make up for in big, bold flavors.
Make the pickled red cabbage: Put vinegar, water, sugar, & salt in a medium saucepan. Bring to a boil over medium-high heat, stirring occasionally to dissolve the sugar. Place the cabbage in a medium, heatproof bowl and pour the vinegar mixture over the top. Stir to submerge the cabbage as much as possible. Let it sit while you prepare the cauliflower, then drain and discard the liquid.
Roast the cauliflower: Arrange a rack in the middle of the oven and heat to 425°F. Place a rimmed baking sheet in the oven while it is heating. Core the cauliflower and cut it into small 1-inch florets that don't have any stem attached. Place the cauliflower in a medium bowl, add the remaining ingredients, and toss to combine. Remove the hot baking sheet from the oven, transfer the cauliflower onto the sheet, and spread into an even layer. Roast until browned in spots but still crisp-tender, stirring halfway through, about 20 minutes total.
For the Tacos: While the cauliflower is cooking, scoop the avocado in a medium bowl and mash. Stir in the yogurt, 1/4 cup of the cilantro, lime zest, and juice; set aside. When the cauliflower is ready, drain off the liquid from the pickled cabbage. To assemble, fill the tortillas with the pickled cabbage and cauliflower, then top with the avocado mixture and remaining 1/4 cup cilantro.
