Rinse the lentils under cold water and set aside.
In a large pot, heat 2 tablespoons of olive oil over medium heat.
Add chopped onions and sauté until translucent.
Stir in minced garlic and cook for an additional minute.
Add diced carrots and celery, cooking for about 5 minutes.
Mix in the diced bell pepper and continue to sauté.
Incorporate the rinsed lentils into the pot.
Pour in the diced tomatoes and vegetable broth.
Add cumin, thyme, salt, and pepper, stirring well.
Bring to a boil, then reduce heat and let simmer for 25-30 minutes until lentils are tender.