Step 1: Preheat your oven to 400°F (200°C). Line a large baking sheet with parchment paper to prevent sticking.
Step 2: In a large bowl, toss the cubed sweet potatoes, carrots, and beets with olive oil, cumin, smoked paprika, chili powder, garlic powder, and salt until evenly coated.
Step 3: Spread the vegetables in a single layer on the prepared baking sheet. Ensure they aren't crowded to allow for proper roasting.
Step 4: Roast for 30-35 minutes, tossing halfway through, until the vegetables are tender and the edges are caramelized and slightly crispy.
Step 5: While the vegetables roast, prepare the avocado slices and warm the tortillas in a dry skillet or over an open flame until pliable and slightly charred.
Step 6: Assemble the tacos by spooning a generous portion of the roasted vegetables into each tortilla. Top with avocado slices, fresh cilantro, and a squeeze of lime juice.
Step 7: Serve immediately while the vegetables are warm and the avocado is fresh.