Gather the ingredients.
Combine marinade ingredients in a small bowl and set aside. Place flat steak, chicken, or tofu in a resealable bag. Pour marinade over top making sure that all surfaces are coated. Seal bag and place in refrigerator. Marinate steak for 1-3 hours, chicken for 1-2 hours, and tofu or vegetables for 15-30 minutes.
While meat is marinating, prepare the lime-cilantro sauce. Place seeded and chopped jalapeño, green onion, cilantro, lime juice, and 1/2 cup/120 mL of the yogurt in a blender or food processor. Puree mixture well. If you intend to use a condiment bottle to drizzle sauce over the nachos, you will need to make sure there are no chunks remaining. Most blenders are efficient all pulverizing vegetable matter, but in case you are left with some unprocessed pieces, run the mixture through a sieve into a bowl. Add the remaining 1/2 cup/120 mL of yogurt and season with 1/4 teaspoon/1.75 mL salt. Transfer into condiment bottle (use a funnel to make this step easier) and store in the refrigerator until nachos are done.
Prepare grill for medium high heat. If using the oven, set to 375 degrees F.
Wash and rinse sweet potatoes. Dry off with a paper towel and chop off pointy ends. Cut into 1/4" slices. Add 2 tablespoons/30 mL of olive oil to cast iron pan. Make sure the entire bottom is well coated. Layer sweet potatoes by stacking them halfway on top of the previous one, working from the outside to the center in a circular pattern. Season with salt and place onto the grill on direct heat for 10 minutes. Move to indirect heat and cook for an additional 15-20 minutes. Watch for burning and adjust heat accordingly.
Once sweet potatoes are cooking over indirect heat, it is time to cook the corn. Remove husks and threads and place onto the grill, rotating corn every 30 seconds to 1 minute, until it begins to blister and char a bit. Don't over do this process or you'll end up with hard, burnt corn. Remove from heat and let cool for a few minutes. Using a sharp knife, carefully cut away kernels and place into a bowl. Cover with plastic wrap until ready to use.
Remove steaks from marinade and place onto grill. If opting for a thin steak, it will be fully cooked in 5-7 minutes. Tofu and other vegetables will be between 3-5 minutes. If using chicken breast, consider cooking this first before the corn. This will take longer and needs to reach a safe temperature of 165 degrees F. in the thickest part of the breast before it is considered done. Once meat (tofu, or vegetables) has cooked through, remove from heat and cut into bite sized pieces.
Now it's time to assemble the nachos while the cast iron skillet is still on the grill. Place the pinto beans on top of the sweet potatoes. Next, the grilled corn kernels. Top with sliced steak (or whatever you choose for this portion), then crumbled queso fresco. Place the lid back on the grill and let it go for 5-7 minutes until everything has warmed through and cheese has melted.
Using heat resistant gloves, carefully remove cast iron skillet and place onto hot pads on a safe surface. The nachos will be sizzling at this point, so let them rest for 5-10 minutes or so. Drizzle liberally with sauce, garnish with cilantro, sliced green onions, and serve. The best way to get them out of the pan is with a spatula. Use a fork to eat these nachos, especially while it's still piping hot.