Preheat Oven To 450°F.
Grease A Rimmed Baking Sheet With Nonstick Spray.
In A Medium Bowl, Combine Sweet Potatoes, Cauliflower, Oil, 2 Tablespoons Lime Juice, 1 Teaspoon Salt, Cumin, Paprika, Chili Powder, And Garlic Powder.
Toss To Evenly Coat All Vegetables In The Seasonings.
Spread On Prepared Baking Sheet And Roast For 20 Minutes.
While Vegetables Roast, Mash Together Avocado, Sour Cream, Remaining 1 Teaspoon Lime Juice, And Remaining ¾ Teaspoon Salt In A Small Bowl.
Set Aside.
Char Tortillas On The Open Flame Of A Gas Stove.
Assemble Tacos With Vegetable Filling And Top With Avocado Mixture.
Serve Immediately.