First, I should say I am coming from a pre-op perspective, so I still have a normal appetite and no restriction from surgery. I'm sharing two recipes that I use most days for my breakfast and lunch. If I eat these earlier in the day, I can barely eat dinner. Combined, this gives you 823 calories and 75g protein in a day. Your jaw is going to hurt after chewing this much salad, and I think it will likely take you most of the day to eat it. There is a lot of fiber. Obviously, I'm not a professional so this is not medical advice, and I have no idea how much you will be able to consume with your bypass. I imagine you would have to go slowly. But there's a good chance, if you even manage to eat all of it, you will not feel like you are starving throughout the day. You could still add a dinner if you need to. The goal here is to give you food that will take away the hungry feeling without adding calories. Natural, unprocessed foods tend to do that better than shakes and bars.
Oh, I top the salad with a fresh squeezed lemon, some salt, and Italian herb blend instead of dressing. And this much salad requires a large serving bowl, not a regular salad bowl. I use a kitchen scale to measure everything. The smoothie fits better in a 20+ oz blender cup as the 16oz is too small. If it's too thick, add some water to get the consistency you like.
(Apologies, this smoothie recipe says flax seed twice. It should be flax and hemp seed, or chia. Also, the mango and strawberry is frozen, and the spinach can be too for convenience)