Heat a large pot over medium heat. Add the diced onion, minced garlic, and grated ginger. Cook for 3 to 4 minutes until the onion softens.
Stir in the curry powder, cumin, and turmeric. Cook for 30 seconds until the spices smell fragrant.
Add the rinsed red lentils, diced tomatoes with their juice, and vegetable broth. Stir everything together.
Bring the pot to a boil, then lower the heat and simmer uncovered for 20 to 25 minutes. Stir a few times until the lentils are soft and the soup thickens.
Taste and add salt and pepper as needed. Ladle into bowls and top with chopped cilantro. Serve with lemon wedges on the side.