Preheat the oven to 400°F. Toss the eggplant cubes with 1 tablespoon of olive oil and spread them on a baking sheet. Roast for 20 minutes until the edges turn golden.
Heat the remaining tablespoon of olive oil in a large pot over medium heat. Add the onion and cook for 5 minutes until it softens.
Stir in the garlic and cook for 1 minute until fragrant.
Add the roasted eggplant, diced tomatoes with their juice, vegetable broth, oregano, basil, and black pepper to the pot. Bring the mixture to a simmer.
Reduce the heat and let the soup cook for 15 minutes so the flavors blend.
Remove the pot from the heat and stir in the lemon juice. Ladle into bowls and sprinkle with fresh parsley before serving.