In a medium bowl, mix the cumin, salt, chili powder, brown sugar, oregano, garlic powder and cayenne pepper.
Cut the pork into 1-inch pieces and toss with the seasoning mix to coat.
In a 12-inch nonstick skillet, heat the oil over medium-high heat. Add the pork, a few pieces at a time, until all are in a single layer in the skillet. Cook for 5 to 8 minutes or until the meat is golden brown and thoroughly cooked, turning to brown on all sides.
Move the pork to one side of the skillet and add the onion. Cook for 1 to 2 minutes or until the meat starts to soften, stirring once or twice.
Meanwhile, heat the taco shells as directed on the package. Cook the corn as directed on the package.
To serve, divide the lettuce evenly among taco shells. Spoon the pork and taco mixture into each taco. Top each taco with the corn, diced tomato and a dollop of sour cream.