Lucky Peach's McAloo Tikki Sandwich

Ingredients

• 2 garlic cloves
• 1 serrano or jalapeño pepper
• 1 1-inch piece fresh ginger
• 2 teaspoons coriander seeds
• 2 teaspoons cumin seeds
• 1 teaspoon ground turmeric
• 1 teaspoon kosher salt
• 1/2 cup fresh or frozen peas
• 3 tablespoons mayonnaise
• 1 tablespoon ketchup
• thinly sliced red onion
• Thinly sliced beefsteak tomato
• 1 cup loosely packed cilantro leaves
• 4 potato hamburger buns
• 1 large russet potato
• neutral oil