Next to blanched veggies such as zucchini and carrot I also have a couple veggies I feed to my clown pleco raw veggies such as swiss chard, baby spinach and kale (she love kale). Lettuce is okay, but it won't provide much nutrition. I actually feed her more leafy veggies than heavier veggies. Though, if you get a carrot that has gone a little woody, blanch it and you have the pleco version of Christmas dinner. XD
I use a veggie clip, that usually works for me raw or blanched.