In a small bowl, mix the taco seasoning ingredients together. Amounts can be adjusted for taste preferences. Add additional chillli flakes if you like it spicy.
Add the beef to a large skillet over medium-high heat. Break the meat apart with a wooden spoon. Add onions, green peppers, and garlic.
Add the taco seasoning to the meat mixture. Stir well. Cook until the meat is cooked through, about 6-8 minutes, stirring occasionally. Drain any liquid or additional grease from pan.
Warm the taco shells according to their package directions.
Fill the taco shells with taco meat. Top with desired taco toppings: mashed avocado, salsa, sour cream, shredded cheese and lettuce.