Heat the olive oil in a large pot over medium heat. Add the onion and cook until it softens, about 5 minutes.
Stir in the garlic and ginger. Cook for 1 minute until fragrant.
Add the cumin seeds, turmeric, and chili powder. Stir for 30 seconds to toast the spices.
Add the tomatoes and cook until they break down slightly, about 3 minutes.
Pour in the kidney beans and vegetable broth. Bring to a simmer and cook for 15 minutes.
Stir in the mustard greens and salt. Simmer for another 5 minutes until the greens wilt.
Taste and adjust salt if needed. Ladle into bowls and top with cilantro. Serve with lemon wedges on the side.