Rinse the red lentils in cold water until the water runs clear. Soak them in water for about 20-30 minutes to help them cook evenly.
In a large pot, heat the olive oil over medium heat. Add the diced onion and sauté until it becomes translucent, about 5-7 minutes. Then, stir in the grated ginger and minced garlic, cooking for another 2 minutes until fragrant.
Add the cumin seeds, turmeric powder, coriander powder, and red chili flakes to the pot. Stir continuously for about 1-2 minutes to toast the spices and release their flavors.
Drain the soaked lentils and add them to the pot along with the can of diced tomatoes (including their juices). Stir well to combine all the ingredients.
Add the reduced-fat coconut milk and vegetable broth to the pot. Bring the mixture to a gentle boil, then reduce the heat to low. Cover the pot and let it simmer for about 20-25 minutes, or until the lentils are tender.
Once the lentils are cooked, stir in the chopped baby spinach and lemon juice. Allow it to wilt for about 2-3 minutes. Season with salt to taste.
Ladle the dal into bowls and garnish with fresh cilantro leaves. Serve it warm with rice or naan for a complete meal.