Brown ground beef in olive oil over medium heat, then drain. Turn heat to low, pour in salsa and taco seasoning, and let simmer for a few minutes.
Chop up onion and spinach. Sauté in olive oil over medium heat for a few minutes.
In the same pan as the onion, add garlic, corn, and black beans and sauté for a few more minutes.
Layer in a bowl as follows: ground beef mixture (bottom), corn and bean mixture, and cheese. Top with avocado and lettuce if desired. Eat with chips or a fork!