Rinse lentils thoroughly, chop onions, garlic, carrots, and celery, and measure out your spices.
Heat olive oil in a large pot over medium heat. Sauté onions for 3-4 minutes until translucent. Add garlic, carrots, and celery and cook until fragrant.
Sprinkle in cumin and smoked paprika, stirring for 30 seconds. Add lentils and bay leaf, coating them in the aromatic mixture.
Add vegetable broth, bring to a gentle boil, then reduce heat to simmer. Cover and cook for 25-30 minutes, stirring occasionally, until lentils are tender.
Adjust salt and black pepper as needed.
Place mashed potatoes on each plate, ladle the lentil stew on top, and garnish with fresh parsley if desired.