Heat the olive oil in a large pot over medium heat. Add the chopped onion and cook until it softens.
Stir in the minced garlic and berbere spice. Cook for one minute until the spices become fragrant.
Add the rinsed lentils, crushed tomatoes, and vegetable stock. Bring the mixture to a simmer.
Cover and cook for 25 minutes, stirring occasionally, until the lentils are tender.
Gently add the tilapia pieces to the pot. Simmer uncovered for 5 minutes until the fish flakes easily.
Taste and add salt as needed. Ladle into bowls and top with chopped cilantro before serving.