Add oil to medium saute pan and turn heat to medium-high. Crumbled tempeh and add to saute pan. Cook for about 3-4 minutes, then add 1/4 cup of the diced tomatoes and the taco seasoning. Add additional salt and pepper if desired and cook for additional 4-5 minutes.
While tempeh is cooking, dice onions and slice avocado into small slices. Drain and rinse beans and corn. Set aside.
Divide lettuce, corn, beans, avocado, and red onion into 3 servings. Top with 1/3 of the tempeh mixture and top with fresh cilantro.