Rinse your brown lentils under cool water and set aside. Heat olive oil in a large pot or Dutch oven over medium heat until it shimmers and smells fragrant.
Add diced onion and sauté for 3-4 minutes until softened and translucent. Stir in minced garlic and cook for another minute, allowing the aromatics to fill your kitchen with incredible fragrance.
Toss in diced carrots and celery stalks, stirring frequently for 4-5 minutes until the vegetables begin to soften slightly. This creates a flavorful base for your cozy lentil weeknight recipe that will develop into something truly special.
Pour in the rinsed lentils, diced tomatoes with their juice, vegetable broth, cumin, paprika, bay leaf, salt, and pepper. Stir well to combine, then bring the mixture to a boil over medium-high heat.
Reduce heat to low and simmer uncovered for 35-40 minutes until the lentils are tender but still hold their shape. The heartwarming slow cooking process allows flavors to intensify and meld into pure comfort.
Stir in balsamic vinegar and fresh spinach, cooking for another 2-3 minutes until the spinach wilts completely into the pot. Taste and adjust seasonings as needed—this is where you make it perfectly yours.
Remove the bay leaf and serve hot in deep bowls. Drizzle with extra olive oil if desired and pair with crusty bread for soaking up the incredible broth.