In a medium pot, add lentils and cover with water. Stir in tomatoes and tumeric. Bring to a rolling boil and simmer until the lentils are soft and cooked, about 30 minutes.
Heat olive oil in a large skillet under medium high heat until hot. Add bell peppers and onions. Cook until starting to soften, about 5 minutes. Add garam masala and stir until fragrant, about 1 minute. Season with salt, cayenne pepper, and lemon juice. Add lentil mixture and chicken stock. Bring to a slow boil and simmer for about 10 mins.