Brown the ground beef in a skillet over medium heat with the chopped onion and minced garlic until the meat is no longer pink. Drain any excess fat.
Transfer the beef mixture to the slow cooker. Add the black beans, diced tomatoes, frozen corn, beef broth, and taco seasoning. Stir to combine.
Cover and cook on low for 6 hours or on high for 3 hours.
Near the end of cooking, cut the corn tortillas into thin strips. Toss them with olive oil and a pinch of salt.
Spread the strips on a baking sheet and bake at 400 degrees for 8 to 10 minutes until crisp.
Ladle the soup into bowls and top each serving with the tortilla strips.