Heat oil in a large saucepan or stock pot over medium-high heat. Add popcorn, and place the lid on the pan. Shake to coat kernels with oil. When the corn starts to pop, shake the pan constantly until the popping stops. Remove from heat.
Drizzle the melted butter over the corn and sprinkle with the chili powder, cumin and salt. Give the pot a couple more shakes to mix seasonings through then pour popped corn into a large bowl.