Heat oil in a large pot over high heat, then add popcorn, cover, and shake pot often. When popping slows, remove from heat until popping stops. Transfer to a large bowl. Melt butter in pot, then add garam masala, cayenne, and turmeric. Drizzle over popcorn, tossing well. Sprinkle to taste with salt.
Note: Nutritional analysis is per serving.