Heat the olive oil in a large skillet over medium heat. Add the diced onion and cook for 2 minutes until it starts to soften.
Stir in the minced garlic and cook for 30 seconds. Add the diced zucchini and cook for 3 minutes, stirring occasionally.
Pour in the diced tomatoes with their juices, the vegetable broth, drained lentils, dried oregano, salt, and black pepper. Stir to combine.
Bring the mixture to a simmer and cook for 6 to 7 minutes, until the zucchini is tender but still holds its shape.
Remove the skillet from the heat and stir in the chopped fresh basil. Taste and adjust salt or pepper if needed before serving.