Set a large pot or Dutch oven on the stove over medium heat. Add the olive oil and let it warm for about 30 seconds.

Add the chopped onion and sliced carrots to the pot. Cook, stirring often, for 5 to 6 minutes, until the onion looks soft and the carrots start to lose their raw crunch.

Add the sliced garlic, ground cumin, ground turmeric, and 1 1/2 teaspoons kosher salt to the pot. Stir for 30 seconds, just until the garlic smells fragrant.

Put the chicken thighs into the pot. Turn them in the onion and spice mixture for about 1 minute so they are coated on all sides.

Add the rinsed red lentils, the diced tomatoes with their juices, and the chicken broth to the pot. Stir once to loosen anything stuck to the bottom.

Increase the heat to high and bring the soup to a boil. This usually takes 4 to 6 minutes.

When the soup boils, lower the heat to medium-low so it gently bubbles. Partly cover the pot and cook for 18 to 22 minutes, until the chicken is cooked through and the red lentils look very soft and are starting to break down.

Use tongs to transfer the chicken thighs from the pot to a plate. Keep the soup simmering on low while the chicken cools for a minute or two.

Shred the chicken on the plate with two forks into bite-size pieces. If you find any large pieces of fat, discard them.

Return the shredded chicken to the pot. Stir it into the soup and let it warm through for 2 minutes.

Add the baby spinach to the pot. Stir until the spinach wilts into the broth, about 1 to 2 minutes.

Turn off the heat. Squeeze the lemon juice from one half of the lemon into the pot and stir well.