In a large pan, add the oil and cook the onion over medium high heat, stirring, until soft, but not brown.
Add in the beef and cook, breaking up, until browned and cooked through. Drain off any excess fat. Stir in the taco seasoning and the fire roasted tomatoes and bring to a simmer. Turn to low and cook, stirring occasionally, until slightly thick.
Meanwhile, prep the toppings: chop the lettuce, shred the cheese, dice the tomatoes, and slice the green onions or chop cilantro.
Assemble the walking tacos by opening up the bags of Fritos and rolling down the top of bag.
Scoop in some saucy meat and top with lettuce, cheese, tomatoes, sour cream, and sliced green onions or cilantro. Enjoy!