Heat olive oil in a large pot over medium heat for 1 minute. Add diced onion, and sauté for 3-4 minutes until softened and fragrant.

Stir in minced garlic, cooking for 30 seconds to release aromatics. Add carrots and celery, sautéing together for 4-5 minutes until vegetables begin softening.

Mix in tomato paste, stirring constantly for 1-2 minutes to caramelize slightly. This step deepens flavors significantly throughout the cooking process.

Pour in crushed tomatoes and vegetable broth, bringing mixture to a simmer. Add red lentils, dried oregano, basil, cumin, bay leaf, salt, and pepper, stirring well.

This tomato lentil soup simmers uncovered for 20-25 minutes until lentils completely soften. Don't skip stirring occasionally to prevent sticking on the bottom.

Taste and adjust seasonings as needed, adding more salt, pepper, or herbs. Stir in balsamic vinegar for subtle sweetness and depth.

Remove bay leaf before serving warm. The hearty tomato soup thickens slightly as it cools.