Begin by rinsing the lentils in a fine mesh sieve to remove any impurities. Transfer them to a medium-sized pot and add a few cups of water. Bring the water to a boil, then reduce the heat to medium and simmer the lentils for approximately 20 to 25 minutes, or until they become tender. The cooking time may vary depending on the type of lentils you're using, so refer to the package instructions for guidance.

Preheat your oven to 300°F (150°C). Spread the walnuts evenly on a rimmed baking sheet and place them in the preheated oven. Toast the walnuts for about 10 to 13 minutes.

Transfer all the toasted walnuts to a food processor and pulse until they are coarsely chopped.

Heat ½ to 1 tablespoon of oil in a large skillet over medium heat. Add the sliced onion and peppers to the skillet and cook for approximately 10 minutes, stirring occasionally, until they become translucent and slightly caramelized. Then, add the minced garlic and the spice mixture, (2 teaspoon cumin, ½ teaspoon oregano, ¼ teaspoon smoked paprika, ½ teaspoon salt) and tomato paste to the skillet and continue cooking for another minute or two, stirring frequently.

Add the cooked lentils to the skillet with the pepper and onion mixture. Cook for a few more minutes until the mixture is heated through.

Pour in the broth. Cook the mixture for approximately 10 to 15 minutes, allowing the lentils to absorb the broth.

Add the chopped, toasted walnuts to the skillet. Gently stir to fully combine all the ingredients, ensuring that the walnuts are evenly distributed throughout the filling.

While the lentil and walnut filling is simmering, take this opportunity to warm tortillas and prepare your choice of vegetable toppings. Add salt to taste.