Add chopped bacon to a large stock pot. Fry bacon over medium heat until crispy.
Depending on how much fat renders off the bacon you might not need to add olive oil, but if pan is a little dry, add olive oil and then toss in the onion, celery, and carrots. Season with a pinch of salt and pepper.
Saute for about 7-10 minutes, or until onion and celery appear translucent. Then add garlic and saute for 1 minute more.
Add tomatoes, lentils, thyme, bay leaves, and chicken stock.
Bring mixture to a boil over high heat. Then cover partially with lid and reduce heat to low.
Simmer for about 50 minutes or until lentils are tender, but not falling apart.
Using an immersion blender partially puree the soup, but be careful not to overdo it- you want to have a decent amount of whole lentils and vegetables for texture. (Note- if you don't have an immersion blender, puree 2 cups of soup in a regular blender and then return to the pot).
Season with salt and pepper to finish.
Garnish with chopped parsley (optional).