With a sharp knife, roughly chop the tempeh block and use your hands to crumble the chopped tempeh into small pieces.
Add the avocado oil to a pan and preheat over medium-high heat. When the oil is hot and shimmering, add the tempeh to your pan. The tempeh should sizzle when it hits the pan. If it does not, remove the tempeh and kick the heat up to high for about 1 minute. Add the tempeh, listen for the sizzle and reduce the heat to medium-high and cook approximately 5 to 7 minutes, stirring occasionally.
As the tempeh begins to brown, add the tomato paste, taco seasoning and salt, and stir well. Cook the mixture for an additional 3 to 5 minutes, and continue stirring to ensure the mixture does not burn.
While the tempeh is cooking, place a tortilla in parchment of wax paper or paper towels. Warm the shells in the microwave for approximately 8 to 10 seconds. Alternative option: You can also warm shells in a skillet over low heat. Place the warmed shells on your plate, add the tempeh crumbles, and garnish with toppings as desired.