Crumble or chop tempeh into small pieces and place in a mixing bowl. Put 1 tablespoon of olive oil, salt, lime juice, chili powder and cumin on the tempeh and mix well.
Let stand 10-30 minutes to marinate, (longer time allows more absorption of the flavor).
Heat the other 2 tablespoons of oil in a large skillet. Add onion and sauté until soft.
Add marinated tempeh and keep mixture moving in the pan until tempeh turns golden brown.
If using frozen corn, be sure to thaw kernels first or briefly blanch to hasten thawing. Combine all ingredients for avocado salsa In a medium bowl. Toss gently maintaining chunky consistency.
Warm corn tortillas in a skillet with just enough butter or olive oil to move it around.
Fill each tortilla with about ¼ cup of tempeh mixture, avocado salsa, lettuce or cabbage.