Eating lettuce every day is just going to make you a starving zombie who craves food all the time. It's not the way to live your life. The best way to lose weight is to change your lifestyle. I've been into nutrition and cooking my whole life as a little interesting side-thing. If you want to eat healthy and look healthy, not crave food like a maniac, you simply have to eat proper vegetables, legumes, fruits, nuts and seeds, grains, mushrooms, fish and chicken if you eat meat. Your body shouldn't starve vitamins and minerals, only for a bit of calories, so avoid sugar, salt, oil, starch, as much as you can. What also matters is how you eat all of that. Make your own list of dishes you like to eat and make them healthy. Eat 3 times a day with the main meal (dinner) being the biggest one. Have fruits in between meals if you feel hungry. Drink self made lemonade with lots of water and tea, some coffee.
I can give you an example of my regular breakfast, to give you an idea of what I'm talking about here. I mash a banana, add 3 spoons of oatmeal, add half a cup of soymilk, half a teaspoon of cocoa, and 2-3 tablespoons of ground nuts and seeds I make (flax, sunflower, sesame. sometimes almond or walnuts). If I need more sweetness, I'd add a teaspoon of good quality honey, but banana is sweet enough for me. A mashed banana can become a really tasty jam in a minute! ;)
My main meals are usually chilli beans or vegetable curries style food, with some grains like millet, barley, buckwheat, corn-grits, and a rich salad made with tomatoes, peppers, onion, spinach, beetroot, sauerkraut, turnip, even lettuce. These two types of food (stew and "risotto" types) are easier to make and can be stored in the fridge for a couple of days. I am a lazy cook, but I like to eat healthy food! ;)