Looks like whitefly damage, they suck sap from under the leaf. Check if you see small white kind of moths around the plant and leaves. Try to move the leaves to see if they fly away from it. Whiteflies are actually tiny moths.
They are difficult to control, I have tried chemicals from the store last year, they all seem not to really work. You might want to try biological control methods, especially when they are on your vegetables. What I tried this year is to sow a lot of plants in the garden that attract ladybirds, I got a special ladybird sow mix. It seems to work, I have seen a lot of these ladybirds in my garden now, and they feed on aphids and whiteflies.