In a large pot, heat chicken broth.
In a large skillet, saute onions and garlic in olive oil for 10 minutes. Add tomatoes, oregano, basil, and pepper. Saute 10 more minutes, until tomatoes are softened. Then Blend all of above in a blender. Add the mixture to hot broth. Add celery, bay leaves, red bell pepper, zucchini, and carrot. Let simmer about ten minutes.
Meanwhile, in skillet, fry tortillas strips in oil until crispy. Drain on paper towels. In the same oil, fry potatoes about 5 minutes. Add to soup mixture with a slotted spoon. Next, add spinach, washed to the soup. Turn off the heat on soup. Salt, if needed.
Place avocados in a serving bowl; adding a few drops of lemon juice to prevent discoloration.
Serve soup by placing 3 to 4 strips tortilla in the bottom of each bowl. Pour hot soup over (be sure to get some of everything, except bay leaves, discard them). Top with avocado and cheese.