You shouldn't need to blanch them, my plecs love pepper as much as courgette. They like red/yellow or orange but not fussed about green. Remove all the pips and use something to keep it in one place in tank, either a fork or the end of a spoon(stainless steel). Make sure its flesh side up and don't worry about the skin as they won't eat it. Then remove whats left in the morning, but you can leave it in for a little longer.
My plecs have veggies 3 times a week, they have deshelled peas once a week as they help keep everything moving through the digestive system.