Heat the olive oil in a large pot over medium heat. Add the diced onion and cook, stirring occasionally, for 4 to 5 minutes until softened and translucent.

Add the minced garlic, cumin, smoked paprika, salt, and pepper. Stir and let it cook for 60 seconds. You want the spices to bloom in the oil before anything wet goes in.

Add the rinsed red lentils, the entire can of diced tomatoes with their juices, and the broth. Stir everything together and bring to a boil over medium-high heat.

Once boiling, reduce the heat to medium-low and simmer uncovered for 18 to 22 minutes, stirring every few minutes. The lentils are done when they are completely soft and have mostly dissolved into the broth, giving the soup a thick, creamy texture. If it looks too thick, add another half cup of broth.

Turn off the heat or drop to the lowest setting. Add the spinach and stir it in. It will wilt fully in about 90 seconds. Do not keep it on high heat or the spinach will go from bright to dull and mushy.

Stir in the lemon juice. Taste and add more salt if needed. Serve hot with crusty bread on the side, or let it cool before portioning into meal prep containers.