Place a large heavy-bottomed pot over medium heat and saute the diced bacon until crispy and fat is rendered.
Remove 2 tablespoons of bacon with a slotted spoon for garnish and set aside.
Add onion, carrots, and celery to the pot with the remaining bacon and fat; saute for 7 minutes until vegetables soften.
Add minced garlic and cook for 1 minute until aromatic.
Pour in the chicken broth and crushed tomatoes, then add the lentils, thyme, smoked paprika, and bay leaf.
Bring the liquid to a boil, then reduce heat to low and simmer, partially covered, for 35 to 40 minutes until lentils are tender.
Remove the bay leaf and stir in the baby spinach until wilted.
Stir in lemon juice and season with salt and pepper to taste.
Ladle into bowls and top with the reserved crispy bacon.