For the spice blend: Stir together the paprika, chili powder, cumin, garlic powder, onion powder and black pepper in a bowl.
For the fajitas: Set a large skillet over high heat. Once the pan starts smoking, add the portobellos, bell peppers, onions, salt and 2 teaspoons of the spice blend. Dry-saute the veggies until you see charring and blistering, about 30 seconds. Add the oil and garlic and continue to cook, stirring often, until softened, 5 to 7 minutes. Remove from the heat and set aside.
Lay out the tortillas and top each with the portobello veggie mix. Sprinkle each with a pinch of the spice blend. Top with sour cream, avocado, cilantro and a squeeze of lime.