If you travel on a budget, like I do, finding a place to eat in London can be a nightmare. That's why I recommend you take the tube to the nearest Ikea and dine in its restaurant.
Meals start at an amazing price of 1 pound and the prices almost never rise above 5 pounds! Breakfast starts at 95p (Sausage, bacon, scrambled egg, hash brown, beans, and tomato). Swedish meat balls start at 3.25 pounds, you can refill your drinks and coffee for free, they have special meals for kids etc.
One might forget about an option like this but Ikea restaurants are always a good place to eat when travelling on a budget.