Heat olive oil in a large Dutch oven or soup pot over medium heat. Add onion, carrots and celery. Cook for 6 to 8 minutes, stirring occasionally, until softened.
Stir in garlic and ginger. Cook for 30 seconds, until fragrant.
Add turmeric, cumin, coriander, salt and black pepper. Stir to coat the vegetables and cook for another 30 seconds to bloom the spices.
Add lentils and vegetable broth (or vegetable broth plus water). Cover and bring to a boil. Once boiling, reduce heat and simmer for 15 to 18 minutes, until lentils are tender.
Stir in the chopped spinach and corn milk. Simmer for about 3 to 5 minutes, until spinach is wilted and the soup is creamy.
Remove from heat and squeeze in lemon juice. Taste and adjust for salt, as needed.
Serve warm with a drizzle of olive oil, a sprinkling of fresh chopped parsley and cilantro, and red pepper flakes (optional) for heat.