Preheat oven to 425°F. Spray a large, rimmed sheet pan with nonstick cooking spray.
In a small bowl, combine chili powder, cumin, smoked paprika, garlic powder, cayenne pepper, and salt.
Arrange cauliflower, sweet potato, and onion in three rows on the sheet pan. Toss with olive oil and half of the seasoning mixture.
Roast 30 minutes, stirring once halfway through.
Add beans, remaining seasoning mixture, and 2 teaspoons of lime juice. Toss all ingredients together to combine. Roast 5 minutes more.
In a small bowl, stir sour cream, remaining lime juice, and hot sauce until combined.
Spoon cauliflower-sweet potato-black beans mixture evenly into corn tortillas.
Top with spicy sour cream sauce and desired garnishes before serving.

Approximate nutritional values per serving (2 tacos with about 1 ¼ cups vegetable-beans mixture and 2 tablespoons sour cream):

280 Calories, 7g Fat (1.5g Saturated), 5mg Cholesterol, 230mg Sodium, 48g Carbohydrates, 5g Fiber, 4g Sugars (0g Added Sugars), 7g Protein