EEEK -- When Lettuce Goes Bad

A word to the wise: Do not eat lettuce that has a flower growing from the center of it! IT WAS SO GROSS... after Googling, I discovered that when lettuce flowers it typically has gone bitter. Lesson learned, so after ripping out half of the lettuce, Dread Pirate Roberts is looking a little lopsided! One half is full of flowering plants (i.e., I'm going to have tomatoes, peppers and melon soon) and the other half is looking weak! I planted some green beans, so hopefully those will take off soon.

What is the key to getting everything harvestable at the same time and keep it that way for 2-3 months???? I'll think on that some more...