Grilled Avocado, Scallion, and Red Onion

INGREDIENTS

• 1 medium red onion, sliced into 1/2-inch-thick rings
• 2 olive oil, divided, plus more for drizzling
• Kosher salt and freshly ground black pepper
• 3 bunches scallions, trimmed
• 2 ripe avocados, halved, pitted
• 1 chile de árbol, crushed, or pinch of cayenne pepper
• Flaky sea salt (such as Maldon)
• Lime wedges (for serving)