Put flour, egg and panko in 3 separate shallow bowls. Season the zucchini slices with salt and black pepper, dredge in flour and shake off excess. Dip in egg, then coat well with panko. Set aside on a cutting board or sheet pan.
Warm a 12-inch skillet over medium-high heat, and add olive oil. When oil shimmers, add zucchini slices in batches and cook until browned on both sides, about 4 minutes, adding more oil if necessary. Transfer zucchini to a paper-towel-lined plate and keep warm.
Add onion, celery, garlic and oregano to hot pan, along with a little more oil, if necessary. Sauté until onion begins to soften, about 3 minutes. Add corn, vegetable broth, milk, cayenne, 1/4 teaspoon salt and a few grinds of black pepper, and bring to a simmer. Turn heat to low so that the soup just bubbles. Cook until vegetables are tender and flavors have blended, about 10 minutes. Taste and season with more salt and black pepper, if needed.
Halve pitas and split them open to make pockets. Place fried zucchini and some hummus into pita halves, along with tomato, lettuce and onion.
Ladle soup into bowls and sprinkle with basil. Serve immediately with the pita sandwich.