Toss sweet potatoes in light coating of olive oil. Sprinkle with salt and pepper. Spread in a single layer on baking sheet. Bake for 30 minutes, or until softened and just beginning to caramelize.
Meanwhile, heat drizzle of olive oil in large non-stick pan, over medium heat.
Add onion, and cook for 3-4 minutes, until softened and slightly browned. Add garlic and cook for 1 more minute.
Add corn. Stir, and spread into a single layer. Cook - without stirring - for 5 minutes or until browned on underside. Stir, spread into single layer again, and cook for additional 3 minutes.
Add 1 tbsp olive oil, 1 cup cotija cheese, chili powder, lime juice, and cilantro. Add salt and pepper to taste. Mix well. Remove from heat, and set aside the Mexican Street Corn.
Warm tortillas on a baking sheet in the oven for 3-5 minutes.
Assemble the sweet potato tacos! Top each corn tortilla with a layer of roasted sweet potatoes, a scoop of Mexican Street Corn, and several slices of fresh avocado. Top with a sprinkle of cotija cheese. Serve.