Same here, just squish them. And you don't need to boil them, just blanch them. Let them sit in boiled water for 15 seconds and you are ready. Also helps if you haven't fed them for a little while, or feed very lightly in the morning, and do peas in the evening, before the main coarse.
Try some zucchini also. When doing cucumbers and zucchini, might take a couple days before they notice it's food, and good food, lol. I generally leave mine in a whole 24 hours. Then if it gets too mushy, replace it. Within a couple days, you will start seeing them eat it.
55G Filstar XP3 - 16" Fire Eel
75G Medium Planted - Filstar XP3 Low Light - Established Feb 2006