Heat the olive oil in a large pot over medium heat. Add the diced onion and cook for 4 minutes until it softens.
Stir in the minced garlic and cook for 1 minute until fragrant.
Add the potato pieces and rinsed lentils to the pot. Pour in the vegetable broth and bring the mixture to a boil.
Reduce the heat to low, cover the pot, and simmer for 25 minutes until the lentils and potatoes are tender.
Remove the lid and stir in the lemon zest, lemon juice, salt, and black pepper. Simmer uncovered for 3 more minutes.
Ladle the stew into bowls and sprinkle with chopped fresh parsley before serving.