Preheat the oven to 350°F (175°C).
Arrange the sliced tomatoes and red onion in an alternating pattern in a small baking dish. Drizzle evenly with olive oil and honey, then season with dried oregano, salt, and black pepper.
Roast for 50–60 minutes, until the tomatoes are soft, slightly caramelized, and the onions are tender. The olive oil should be infused with tomato juices and herbs.
While the tomatoes are roasting, toast the sourdough slices until golden and crisp.
Crumble and gently spread the feta over the warm toast slices.
Spoon the roasted tomatoes and onions over the feta, making sure to drizzle some of the flavorful olive oil from the baking dish over each toast.
Finish with fresh oregano leaves and serve immediately.