I grew lettuce last year and it was good for a while, but then it bolted and got quite bitter. The leaf lettuce less-so than the head lettuce. I'll be devoting more room to tomatoes and peppers this year and probably less to the greens, though I am giving Swiss chard a try
That is in the nature of lettuce, to bolt once the weather gets hot. The earlier you get it started, the longer you have lettuce. I plant lettuce seed directly in the ground early in March ("as soon as the soil can be worked").
Then you can start it again late in the season for a fall crop.
But yes, I love the chard, which doesn't mind the heat and just keeps going all season!