In a large pot over medium heat, warm olive oil until shimmering. Add onion and garlic, sauté until softened and fragrant, about 3 minutes.

Toss in carrots and celery, stirring for 5 minutes until veggies begin to soften and gain a touch of golden color on the edges.

Sprinkle cumin and smoked paprika over the veggies, cook 1 minute until fragrant and spices turn a deeper, earthy red hue.

Pour in diced tomatoes and vegetable broth, scraping up brown bits from the pot. Stir to combine, then bring mixture to a gentle boil.

Add brown lentils and bay leaves, reduce heat to low, cover and simmer for 25 minutes until lentils are tender.

Stir in diced potatoes, cook uncovered an additional 15 minutes until potatoes are soft and the stew reaches a thick, hearty consistency.

Fold in spinach or kale, stirring until just wilted, about 2–3 minutes to preserve vibrant green color. Remove bay leaves before serving.

Taste and season with salt and pepper, then let stew rest off heat for 5 minutes to meld flavors fully before ladling into bowls.