I just made a post about this earlier today. I just purchased some scratch mix that has a small amount of uncooked split peas and I wasn't sure if they would hurt the chickens. Someone posted back that they also purchased some scratch that has split peas in it and their chickens are doing well. I wouldn't feed the chickens a lot of uncooked split peas, but it seems like if they're in a scratch mix designed for birds, they're ok. As a general rule don't feed your birds uncooked beans. If you're wanting to feed them split peas that aren't part of a scratch mix, you'll definitely want to cook them first.
Split peas & lentils do not need to be cooked and are fine for chickens. They are 22-24% protein, so really good for upping the protein. I have fed mine whole field peas and they are fine, even the bantams. They are not their favorite, but they eat them.