Preheat the oven to 400 degrees. Place the sweet potato rounds on a parchment paper-lined baking sheet and sprinkle with sea salt. Bake for about 25 minutes, and flip the potatoes over. Bake for about 20 minutes longer or until slightly browned. Set aside.
Add the oil to a large skillet over medium heat. Add the onion, pepper and radish or zucchini to the pan, along with a light sprinkle of sea salt and a dash of chili powder. Sauté the vegetables until the onions are translucent and a bit golden, about 10 minutes. Remove from the heat.
Assemble the nachos by layering sweet potato rounds on serving plates, and layer with the vegetables, 1/3 cup of black beans and any favorite toppings. Finish with a squeeze of fresh lime juice.