In a skillet, heat the olive oil over medium heat. Add the diced onion and sauté for about 4-5 minutes, or until the onion becomes translucent. Stir in the minced garlic and sauté for an additional minute until fragrant.
Next, add the drained and rinsed black beans to the skillet. Sprinkle in the cumin, smoked paprika, cayenne pepper, kosher salt, and freshly ground black pepper. Stir well to combine all the ingredients.
Add the tomato paste and water to the skillet. Stir everything together, allowing the mixture to simmer for about 5 minutes. This will help the flavors meld beautifully.
While the bean mixture is cooking, warm the taco shells according to package instructions. This step is crucial for achieving that perfect crunch!
In a small bowl, mash the avocado with the lime juice, a pinch of kosher salt, and freshly ground black pepper to taste. This creamy topping will add a delightful contrast to the hearty filling.
To assemble, spoon the black bean mixture into each taco shell. Top with the mashed avocado, diced plum tomato, and shredded romaine lettuce. Finally, sprinkle shredded cheddar cheese over each taco.