Whiteflies can be a common pest of leafy greens, and what you're seeing are juveniles, not eggs. (Juveniles are very flat-bodied.) As noted by the linked page, you can spray the foliage with either horticultural oil (neem being one type among several options) or insecticidal soap. These are contact-type insecticides, which means they must contact the pest directly to work, so be thorough when spraying and coat all of the upper and lower leaf surfaces, following the label directions on the product chosen. (Make sure it's labeled for use on vegetables.) Do not spray the leaves already harvested, only those still on the live plant; the leaves harvested can have the insects removed by rubbing them (with fingers or a spare toothbrush) under running water in the sink.

Miri