Prepare the Oven and Vegetables: Preheat your oven to 425°F (220°C) and line a large baking sheet with parchment paper or aluminum foil to prevent sticking and simplify cleanup. In a bowl, combine the diced zucchini, chopped red onion, bell pepper, and halved cherry tomatoes. Drizzle the vegetables with olive oil, sprinkle 1 ¾ teaspoons of chili powder, and add a pinch of salt. Toss everything gently until the vegetables are evenly coated, then spread them out in a single layer on the prepared baking sheet.
Roast the Vegetables: Place the baking sheet in the preheated oven and roast the vegetables for about 20 minutes. Every 7-8 minutes, gently stir the veggies to promote even cooking and caramelization. The goal is to achieve tender, slightly charred edges for maximum flavor.
Add Black Beans to Roast: While the veggies roast, toss the black beans with the remaining ¼ teaspoon chili powder and a light drizzle of olive oil. After the vegetables have roasted for 20 minutes, add the seasoned black beans to the baking sheet, mixing them gently with the veggies. Return the sheet to the oven and roast everything together for an additional 5 minutes, until the beans are warmed through and the vegetables are perfectly tender.
Make the Cilantro Sauce: While the roasting finishes, prepare the sauce by placing sour cream, lime juice, jalapeño, cilantro leaves, and a pinch of salt in a blender or food processor. Blend until completely smooth and creamy. Taste the sauce and adjust with more lime juice or salt if needed.
Warm the Tortillas: Wrap the tortillas in two stacks, each covered tightly with aluminum foil. Place them in the oven during the last 10-15 minutes of cooking to warm through evenly without drying out.
Assemble Your Tacos: Once everything is ready, lay out the warmed tortillas and fill each with a generous scoop of the roasted veggie and bean mixture. Top with cubed avocado, a spoonful of creamy cilantro sauce, and a few pickled red onions if desired.