Heat the oven to 400°F. Line a baking sheet with parchment paper.
In a large mixing bowl combine the cauliflower florets, onion, olive oil, chile powder, paprika, and salt. Toss well.
Spread the veggies in an even layer on the baking sheet. Roast for 35-45 minutes, or until the veggies are soft.
Meanwhile, prepare a cabbage slaw. In a medium bowl combine the cabbage, mayonnaise, lime juice, and chipotle powder. Mix well.
Open the tacos and spoon some of the cabbage slaw and cooked veggie filling into them, add a few slices of radish.
Sprinkle with chopped green onion and cilantro. Serve with salsa verde on the side.