Use kitchen shears to cut long whiskers and sharp head point off of the shrimp. Place cornstarch in a bowl. Roll in cornstarch to coat lightly and evenly, brushing off excess.
Heat 2 tablespoons peanut oil in a skillet over medium-high heat. Add shrimp and saute until red and golden, about 2 minutes per side. Transfer shrimp to a paper towel-lined plate and wipe out skillet.
Heat remaining peanut oil in the same skillet. Add garlic, onion, and ginger; cook and stir until fragrant and soft, about 1 minute. Add scallions, jalapeno, and coated shrimp. Cook and stir for 30 seconds while seasoning with most of the salt and pepper. Garnish with remaining salt and pepper before serving.
