Preheat oven to 425℉ degrees and line a baking sheet with parchment paper. You may need to use two pans depending on their size because you don’t want to overcrowd the cauliflower pieces during roasting.
In a large mixing bowl, toss the cauliflower florets in the olive oil to evenly coat. Add the cumin, chili powder and a hefty pinch of salt and pepper and toss to combine. Pour the cauliflower out onto the prepared baking sheets in a single layer, making sure the florets are not crammed together. Roast for about 45 minutes, until the bottoms of the florets have browned and are extremely tender with crispy edges. Remove from the oven.
In a large mixing bowl, whisk together the chipotle peppers and ¾ cup sour cream. Add the cauliflower and toss to evenly coat.
Assemble the tacos starting with the cauliflower, followed by red onion, additional sour cream and cilantro.