Pour the buttermilk into a large casserole dish or bowl and season with sea salt and black pepper.
Add the chicken pieces to the buttermilk, turn to coat, cover, and refrigerate for 1–2 hours or overnight.
Preheat the oven to 180°C (365°F) and position a rack in the middle of the oven.
In a food processor, combine the cornflakes, panko, olive oil, cayenne (if using), ground garlic (if using), dried oregano, and a pinch of salt and pepper; pulse until the mixture is finely crumbled. Transfer to a large bowl.
Remove each chicken piece from the buttermilk, shaking off excess, then press into the crumb mixture to coat evenly, patting gently so crumbs adhere.
Line a baking tray with parchment paper and lightly brush or spray with olive oil; arrange the coated chicken tenders in a single layer without crowding.
Bake for about 20 minutes, or until the chicken reaches an internal temperature of 73°C (165°F) and the coating is golden and crisp.
Remove from the oven and serve immediately with your favorite dips.
