Gordon Ramsay's Famous Chicken Sandwich (Crispy Baked)

Ingredients

• 1 1/4 lb (565 g) chicken breast tenders or thin breast fillets
• 1/2 cup (60 g) wholemeal flour
• 3/4 cup (180 ml) buttermilk
• 3 cups (75 g) puffed rice cereal, lightly crushed
• 2 teaspoons garlic powder
• 2 teaspoons onion powder
• 4 teaspoons paprika
• 1 teaspoon dried sage
• 1 teaspoon fine sea salt, divided
• 1/2 teaspoon black pepper
• 1 tablespoon olive oil or cooking spray for the baking sheet
• 1/3 cup (80 g) Greek yogurt
• 1/2 garlic clove, finely grated
• 1 teaspoon cider vinegar, plus more to taste
• Pinch of salt and black pepper
• 4 wholemeal sandwich buns, split
• 1 ripe avocado, peeled, pitted, and sliced
• 2 cups (120 g) shredded iceberg lettuce
• Mexican-style hot sauce, to serve