Begin by preheating your oven to 425°F (220°C). Line a baking sheet with parchment paper to prevent sticking.
In a large mixing bowl, combine the all-purpose flour, baking powder, salt, garlic powder, and black pepper. Whisk these dry ingredients together until well blended.
Add the cold cubed butter into the flour mixture. Use your fingers or a pastry cutter to work the butter into the flour, continuing until the mixture resembles coarse crumbs with some pea-sized pieces of butter still visible.
Fold in the shredded sharp cheddar cheese and finely chopped jalapeños, ensuring they are evenly distributed throughout the mixture.
Gently pour in the buttermilk and add the sliced green onions (if using). Stir the mixture carefully, just until combined; be cautious not to overmix. The dough should feel slightly sticky.
Using a large spoon or an ice cream scoop, drop generous spoonfuls of the biscuit dough onto the prepared baking sheet, spacing them about 2 inches apart to allow room for spreading.
Place the baking sheet in the preheated oven and bake for 12-15 minutes. The biscuits are done when they are golden brown on top and baked through.
Once baked, remove the biscuits from the oven and let them cool on the baking sheet for a few minutes before transferring them to a wire rack or serving plate.