Preheat oven to 350 degrees Fahrenheit. Line a baking sheet with parchment paper. Place handfuls of chips on the baking sheet and distribute evenly, minimizing the gaps between chips.
Sprinkle generously and evenly with shredded cheese. Sprinkle veggies over the cheese, then sprinkle on the feta. Repeat to build layers if you’re feeding a crowd. Bake until the cheese is melted and bubbling, about 15 minutes for a single layer or 20 minutes for multiple layers. Serve immediately on a heat-safe surface (transfer the parchment paper to a serving platter or at minimum, warn eaters of the hot baking surface).
While the nachos are baking, make the guacamole. Slice the avocados in half length-wise, running your knife around the pit. Twist the halves in opposite directions, then pull apart the halves. Dislodge the pits and use a large spoon to scoop the flesh into a medium bowl. Sprinkle with lime juice, then mash the avocado with a large fork or potato masher. Stir in the garlic, salt, cilantro, coriander, jalapeño (if using) and chopped radishes. Serve immediately.