my flock love split peas too, especially pigeon peas (which I just ferment, don't cook). Peas + grains make a complete protein. My flock also eats white, blue, green and maple peas (all fermented with the grains).
Although you're going to sprout the lentils, I hope you'll try fermenting one...
I have added them to a ferment mix in years past, inclusion rate of not more than about 10%, and they're not toxic, but there's something in them that is not great and I do not normally include them now. Cooked I'm sure they're fine, and a good source of protein. I'll try to find what I read...