Preheat the oven to 425 degrees and line a baking sheet with parchment paper.
Add all of the cauliflower ingredients (except for the cauliflower & shallot) to a bowl and mix to combine. Add the florets and toss to coat evenly. Transfer to the baking sheet and add the shallots. Spread out into an even layer and place in the oven for 20 minutes. Toss and cook for another 5-10 minutes, or until charred on the edges.
Meanwhile, prep the yogurt sauce. Add the ingredients to a bowl and mix to combine. Set aside.
Add the avocados to a bowl and gently mash. Add the rest of the guac ingredients and mix to combine. Taste and adjust seasonings as needed.
Heat the tortillas over an open flame or in a pan. To assemble, spread some guac on each tortilla and top with cauliflower, red onion, chipotle sauce and cilantro. Serve with lime wedges on the side.