Heat oil in a large skillet over medium-high heat. Add mushrooms and onions; cook 6 to 8 minutes, stirring occasionally, until soft. Add garlic, adobo sauce, chili powder, smoked paprika, cumin, and salt; cook 2 minutes, until aromatic.
Add lentils, vegetable broth, and soy sauce; stir to combine. Gently simmer for 5 to 6 minutes, stirring occasionally, until liquid is completely reduced. Remove from heat and adjust seasonings as needed. Spoon into tortillas and top with garnishes of choice, or see text in post for additional serving suggestions.
To Make Ahead. You can fully prepare the vegetarian taco filling up to 2 days ahead. The flavor will stay sharp, and the texture meaty.To Store. Place leftover taco filling in an airtight storage container in the refrigerator for up to 4 days. Store tortillas and toppings separately.To Reheat. Gently rewarm filling in a large skillet over medium heat. You can also reheat the filling in the microwave, and pile into tortillas just before serving. I suggest warming the tortillas fresh each time, as they will likely harden after being warmed and then refrigerated.