Preheat oven to 400 degrees F. Coat a large rimmed baking sheet with cooking spray.
Combine oil, chili powder, cumin, onion powder and 1/8 teaspoon salt in a large bowl. Add cauliflower and gently toss to coat. Spread the cauliflower in a single layer on the prepared pan. Bake until tender and starting to brown, 15 to 20 minutes.
Meanwhile, combine tomato, avocado, cilantro, jalapeños, onion and the remaining 1/8 teaspoon salt in a small bowl.
Top the cauliflower with beans, chicken and cheese. Bake until the cheese is melted, about 5 minutes.
Serve the "nachos" topped with the salsa and cabbage.