Coat the bottom of a medium saucepan with oil and place it over medium heat. When the oil is hot, add the onion and sauté until softened, about 5 minutes. Add the garlic, cumin and ancho chile powder. Cook 1 minute more, until fragrant. Add the broth and lentils, and bring to a simmer. Allow to simmer, uncovered, until the lentils are tender but not mushy, about 30 minutes, adding a bit of water to the pot during cooking if needed. Remove from heat and season with salt and pepper to taste.
Make the roasted veggies:
While the lentils simmer, preheat oven to 400°F. Place the cauliflower, bell pepper and onion into a roasting pan or oven-safe skillet. Add the olive oil and toss to coat. Place in oven and roast until the cauliflower is tender and browned in spots, about 25 minutes, flipping once about halfway through cook time. Remove from oven and toss with lime juice and cilantro. Season with salt and pepper to taste.
Make the tortilla strips:
Arrange the tortilla strips on a parchment-lined baking sheet and lightly spray with olive oil. Sprinkle lightly with salt. Place in the oven with the veggies and bake until the strips begin to brown and crisp, about 8 minutes.
Make the tahini cheese sauce:
Whisk all the ingredients together in a small bowl, thinning with as much water or milk as needed to reach desired consistency. Taste test and adjust seasonings to your liking.
Assemble the bowls:
Divide the lettuce among 4 bowls, then top with diced tomatoes, lentils, roasted veggies and tortilla strips. Drizzle with tahini cheese sauce and serve.
Feel free to swap out any of the roasted veggies with whatever you've got on hand or is in season. Broccoli, zucchini or corn would all be great choices.
Add any or all of your favorite taco toppings, like avocado slices, jalapeño peppers or jarred salsa.