I grew lettuces in my garden every year in the backyard of our old house.
I'd dig a trench, mix in compost from the previous year's apple tree's detritus, then rake it out to a long, mounded - then somewhat flattened - row of about 4 meters long, and a half meter wide, keeping the soil as fluffy as possible.
I would then use my middle and index fingers like a plow to make 2 long, shallow indentations along the length of the mounded/flattened row. Barely the depth of the first digit of my fingers.
Then I'd sprinkle whole packets of cheap lettuce seeds along each indentation, and carefully brush just a bit of soil over them.
The rows were gently watered from a wide headed watering can so as not to wash out the seeds from their rows for a few days.
As the seeds germinated, I was able to first pluck out handfuls of extravagant "micro-greens" to eat. Actually, I was just thinning out the rows.
I continued for a week or three more by picking out more micro, then baby greens as they grew, each time thinning the rows to allow certain head type lettuces to continue.
Finally, when head types such as Romaine, Boston Butterhead, and Bibb start to form, they were grown and picked until some started to bolt to seed in the beginning of the hotter days of summer.
The trick was to get the tomatoes and cukes to produce early enough before the lettuces ended so that we could have a proper salad entirely from the garden.