Step 1: Preheat your oven to 300°F (150°C). Line a large baking sheet with parchment paper or a silicone baking mat.
Step 2: Peel and thinly slice the yellow onions into rings, about ⅛-inch thick. Separate the rings and set aside.
Step 3: In a small bowl, combine the paprika, coarse sea salt, garlic powder, seasoning salt, and ground black pepper.
Step 4: In a large bowl, toss the onion rings with avocado oil until lightly coated. Sprinkle the spice mixture over the onions and toss again to ensure even coating.
Step 5: On the prepared baking sheet, arrange the seasoned onion rings in a single layer. Try not to overlap them too much to ensure even crisping.
Step 6: Sprinkle the freshly grated Parmesan cheese generously over each onion ring, ensuring the cheese covers the onion and forms a perimeter for a crisp 'chip' effect.
Step 7: Bake for 25-30 minutes, or until the Parmesan is golden brown and crispy, and the onions are tender. Keep a close eye on them during the last few minutes to prevent burning.
Step 8: Remove from the oven and let cool completely on the baking sheet. As they cool, the chips will crisp up even further. Serve immediately or store for later.