Roll out the pizza dough on a floured surface until about 1/4 inch thick. Transfer to a preheated pizza stone or a baking sheet lined with parchment paper. Preheat oven to 450°F (232°C).

Pat dry the cod fillets thoroughly and dredge in flour. Heat vegetable oil in a sauté pan over medium heat and cook the cod for 2-3 minutes on each side until golden.

In a mixing bowl, combine diced tomatoes, drained sun-dried tomatoes, chopped green onions, celery, and sliced red onion. Drizzle with olive oil and balsamic vinegar, season with salt and pepper, and mix well.

Place the rolled-out flatbread in the oven and bake for approximately 10 minutes until slightly golden and firm.

Remove flatbread from the oven, sprinkle crispy cod and spoonfuls of tapenade mixture over it, then top with shredded mozzarella.

Return the assembled pizza to the oven and bake for an additional 5-7 minutes until the cheese is melted and bubbly.

Let the flatbread pizza cool for a couple of minutes. Slice into portions and serve warm.