To prepare the black beans, bring a medium saucepan with olive oil to medium heat. Add the onions and cook until they are translucent (about 2-3 minutes). Then, add the black beans and season with cumin. Cook for 5 minutes or until they are warm. Remove from heat and set aside. Allow them to cool for a few minutes before adding them to the salad.
To prepare the vegan green goddess dressing, add the avocado, cilantro, lime, agave, garlic, cumin, salt, and olive oil to a food processor or blender. Blend until smooth and creamy. Set aside. You may taste the dressing and if you like a spicier dressing, feel free to add a slice or two of jalapeño and blend again.
To assemble the taco salad, add the romaine to a large bowl. Top with the cooked and cooled black beans, corn, diced avocado, crushed tortilla chips, tomatoes, and onion. Add about half of the green goddess dressing to the bowl, toss and add more dressing as desired. If you use half of the dressing in this recipe, it'll add about 90 calories per serving. If you use all of it, it'll add about 180 calories per serving.