Heat the olive oil in a large pot over medium heat. Once it's shimmering, you're ready for the next step.

Sauté the aromatics. Add the diced onion and cook for about 4-5 minutes until it becomes translucent and soft. Toss in the minced garlic and cook for another minute until fragrant.

Add the vegetables. Throw in your carrots and celery, stirring everything together. Let them cook for about 3-4 minutes to soften slightly.

Toast the spices. Sprinkle in the cumin, turmeric, and red pepper flakes if using. Stir constantly for about 30 seconds to wake up those flavors.

Add the lentils and broth. Pour in your rinsed red lentils, vegetable broth, and drop in the bay leaf. Give everything a good stir.

Bring to a boil then reduce the heat to a gentle simmer. Let the soup cook uncovered for about 20-25 minutes, stirring occasionally, until the lentils are completely tender and starting to break down.

Add the lemon. Remove the bay leaf and stir in the lemon juice and zest. This is where the magic happens! The soup will brighten up immediately.

Wilt in the spinach if you're using it. Just stir it in and let it wilt for a minute or two.

Season to taste with salt and black pepper. Start with about 1 teaspoon of salt and adjust from there.

Serve hot with a garnish of fresh herbs and maybe an extra squeeze of lemon on top!