Add the oil to the frying pan or skillet and place the pan on a medium to high heat. Once the oil has heated, add in the mince and start to break up the meat. Cook for 2 minutes then add in the chopped onions and chopped garlic. Keep turning the mince until all the beef is brown and you can no longer see any pink.
To the beef, add the salt, black pepper, garlic powder, onion powder, paprika and oregano then mix them into the beef. Mix in the tomato puree then pour in the stock. Reduce the heat to low to medium and allow to cook for 25 minutes. After 25 minutes, increase the heat and continue to cook until all the water evaporates. When the water has completely dried out, remove the pan from the heat and set aside while you prepare the taco shells and salad.
Warm the taco shells in the oven according to the instructions on the packaging. Remove from the oven and break them up into pieces. To assemble the salad, add the romaine, red onions and cherry tomatoes to the bowls. Top with the beef then sprinkle the cheese onto the beef. Add the sliced avocados and add in the broken taco shells. Mix together the soured cream, mayonnaise and chives then add to the salad and serve immediately.