Preheat your oven to 425°F (220°C). Line a large baking sheet with parchment paper.
In a large bowl, toss the sweet potatoes, bell peppers, and onion with olive oil, chili powder, cumin, paprika, salt, and pepper until evenly coated.
Spread vegetables in a single layer on the prepared baking sheet. Avoid overcrowding to ensure proper roasting.
Roast for 25-30 minutes, stirring halfway through, until vegetables are tender and slightly caramelized at the edges.
While vegetables roast, prepare the lime crema by whisking together Mexican crema, lime juice, minced garlic, and salt in a small bowl. Refrigerate until ready to use.
Warm the tortillas either in a dry skillet over medium heat or wrapped in foil in the oven during the last 5 minutes of vegetable roasting.
Assemble tacos by filling each tortilla with roasted vegetables, drizzling with lime crema, and topping with fresh cilantro, avocado slices, and queso fresco if desired.