Remove the rosemary from the olive oil and finely mince the leaves. Discard the stems.
Add the lemon juice and minced rosemary to the oil and whisk until combined. Slowly add the sea salt. Taste the dressing as you slowly whisk in the salt.Some people like a lot of salt, others don't like any. If you add too much you can't take it back, so go slowly.
Put the chickpeas in a large bowl and add the dressing. Stir until the chickpeas are coated in the dressing.
Serve at room temperature.