Preheat the oven to 400° F
In a large sauté pan, heat the 4 tablespoons olive oil over medium heat. When the oil is hot, add the onion and garlic. Season with salt and pepper. Sauté, stirring for about 5-8 minutes or until the onion and garlic are softened. Reduce the heat to avoid the vegetables from browning. Remove from heat and set aside.
Bring a large pot of water to a boil. Add the whole tomatoes and cook for about one minute to loosen the skins. Transfer to a bowl of cold water, and drain. Core the tomatoes and slip the skins off. Cut the tomatoes into thick wedges.
Return the sauté pan with the onion and garlic mixture to a burner over medium-high heat. Add the tomato wedges, salt, pepper, and red pepper flakes. Cook and occasionally stir the mixture for about 10 minutes to soften the tomatoes. Transfer to an oven proof baking dish.
In a medium bowl add the shrimp, one tablespoon olive oil, salt and pepper. Stir to coat the shrimp.
Arrange the shrimp evenly in one layer over the tomato mixture. Crumble the feta and scatter it over the shrimp. Sprinkle the top with oregano.
Bake for 10-15 minutes or until tomatoes are bubbling and the cheese is slightly golden. Let rest for 5 minutes. Sprinkle with fresh mint ot serve.