Preheat the oven to 400℉.
Place the tomatoes, garlic cloves, onions, and oregano leaves on a large sheet tray. Drizzle with oil and season with salt, pepper, and crushed red pepper flakes (if using). Toss until well combined and coated in the oil, then spread in a single layer across the pan. Transfer to the oven and roast until the tomatoes are blistered and begin to burst, and the onions and garlic and tender, about 40 minutes, tossing about halfway through so that everything cooks evenly.
Remove from the oven and let cool for 5 minutes. Carefully transfer the contents on the sheet pan and any of the juices to a high-speed blender. Add the feta and blend until smooth, about 1 minute, or to your desired consistency.
Pour the blended tomato soup into a large pot. Add the chicken broth and lemon juice. Cook over medium heat to warm the soup back up, stirring often. Taste and adjust seasonings, if desired.
To serve, ladle into bowls and top with a touch more crumbled feta, lots of fresh dill, and few cracks of pepper and a drizzle of olive oil! Enjoy!