Blend all the ingredients for the sauce in a blender or food processor. Adjust salt and lime juice to taste.
To make the taco filling
Heat oil in a skillet, add the minced garlic and sliced onions, and sauté for a minute.
Add the chopped vegetables, seasonings, and diced green chilies, and sauté on high heat until the vegetables are cooked through but not too soft, about 5 to 6 minutes.
Add the corn, black beans, and chopped cilantro, and mix.
Set aside.
To serve
Heat the corn tortillas on the stove, and place the vegetable and bean filling in the middle of the tortilla.
Add the cilantro avocado sauce, diced avocados, chopped cilantro, and crumbled cotija cheese, and serve with lime wedges on the side.