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 berbere seasoning. Cook for 1 minute until the spices smell fragrant.
Add the rinsed lentils, sweet potato cubes, diced tomatoes with their juice, vegetable broth, and salt. Stir everything together.
Bring the mixture to a boil, then lower the heat to a simmer. Cover the pot and cook for 25 minutes, stirring once or twice.
Remove the lid and simmer uncovered for 10 more minutes until the lentils are tender and the stew has thickened.
Ladle into bowls and top each serving with chopped cilantro.