Special equipment: A spice grinder
Make the Spice Mix: Put half the tomato strips in a single layer on a microwavable plate. Microwave in 30-second increments, checking the texture in between, until they begin to harden but are still red and slightly pliable, 1 to 2 minutes. (They may begin to brown and taste bitter if cooked too long.) Let sit until cool and completely hardened, about 2 minutes. Repeat with the remaining tomato strips.
Transfer the cooled tomato strips to a spice grinder, and grind to a powder. Discard any pieces that won't grind. Add the nutritional yeast, chili powder, cumin, oregano, cayenne and 1 teaspoon salt, and grind to a fine powder.
Make the taco popcorn: Heat the oil in a large pot over medium heat. Add the popcorn kernels. When one pops, cover the pot, and cook, shaking the pot constantly, until the popping subsides to 1 pop every 20 seconds. Pour in the melted butter, and toss to coat. Add 2 heaping tablespoons of taco spice and 1/2 teaspoon salt, and toss again to coat.
Store the remaining taco spice blend at room temperature in an airtight container for up to 2 weeks. (You'll have enough to make 3 more batches of popcorn.)
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