Meanwhile, add onion, poblano and bell pepper to the bowl with the reserved oil and spices; toss to coat. Move the sweet potatoes to one half of the baking sheet and add the onion mixture in an even layer to the other half. Bake until the sweet potatoes are tender and the peppers and onions are just tender, about 10 minutes. Switch oven to broil on high; broil until the peppers and sweet potatoes begin to char, 3 to 5 minutes. Season with salt. Divide the vegetable mixture among tortillas; top evenly with avocado, radishes, cilantro and queso fresco. Serve with lime wedges.