Preheat oven to 425°F (220°C)
Pound chicken breasts to ¼-inch thickness
Cut or cube chicken into bite-sized pieces
In a zip-top bag, mix garlic powder, onion powder, paprika, 1 tsp sea salt, ½ tsp black pepper, and the cubed chicken
Seal and toss gently until coating is even
Sift flour, baking powder, sugar, and sea salt into a bowl
Add 75g chilled butter and cut in using a pastry blender until mixture resembles coarse crumbs
Drizzle 6 tbsp buttermilk into the bowl and mix with a fork until a soft dough forms
Knead dough 3-5 times on a floured surface
Roll dough to ¾-inch thickness and cut into small biscuit shapes
Bake biscuits for 10–12 minutes until golden and flaky
Let chicken rest in refrigerator 10–15 minutes after seasoning
Sear chicken in a skillet over medium-high heat until golden and cooked through
In a bowl, combine mayonnaise, whole grain mustard, and remaining ½ tsp sea salt
Spread mixture into the base of each warm biscuit, add a chicken piece, pickle slice, and top with another biscuit