Heat the olive oil in a large pot over medium heat. Add the diced onion and cook until it softens.
Stir in the garlic, ginger, cumin seeds, turmeric, garam masala, and chili powder. Cook for one minute until the spices smell fragrant.
Add the rinsed lentils, cubed potatoes, diced tomatoes, and vegetable broth. Bring the mixture to a boil.
Reduce the heat to low, cover the pot, and simmer for 25 minutes until the lentils and potatoes are tender.
Stir in the frozen peas and cook for another 5 minutes. Season with salt and pepper to taste.
Remove the pot from the heat. Serve the stew topped with chopped cilantro and lemon wedges on the side.