In a large skillet, heat oil, then add chopped onion. Cook just until onion begins to turn translucent, then add minced garlic.
In a large pot, cook pasta in salted, boiling water until just done (about 9 minutes. It will cook a little more in the oven). This can be going on while you're assembling the ingredients in the skillet.
Returning to the skillet, add beef and taco seasoning. Once the beef is cooked through, then add tomatoes, corn, beans, and sour cream. Stir until well combined. Add shredded cheese. Then add drained, cooked pasta.
Transfer to a lightly greased 9x13 baking dish. If desired, sprinkle more shredded cheese over the top. Bake in a 350 degree oven for about 20-25 minutes, or until bubbly and cheese is golden.
Serve with tortilla chips, sour cream, and salsa, if you like. Enjoy! =).