Soak bread in water in a large shallow dish until softened completely; remove from dish and squeeze as much water from bread as possible.
Heat 1 tablespoon olive oil in a non-stick skillet over medium heat; cook and stir onion, spinach, and garlic in the hot oil until the onion softens, about 5 minutes.
Mix the onion mixture with softened bread, tuna, mushrooms, zucchini, celery, eggs, dill, salt, pepper, basil, and oregano in a large bowl until combined. Form the mixture into about 24 thin, palm-size patties.
Heat 1 tablespoon olive oil in a large skillet over medium heat; cook the patties in the skillet until cooked through, 2 to 3 minutes per side.