oh man, I love split pea soup....although DH hates it with ham, so I make a vegan version that is awesome.
I've substituted split peas (both green and yellow) for lentils - they have a bit different flavor, but are still pretty good in most everything I've used them in - with one exception, lentil tacos. Let's just say that split pea tacos were not the hit I was expecting them to be....oh well, I guess that is what you get for not checking ingredients before promising a meal
I have a recipe for a lentil loaf that I sub split peas in for some or all of the lentils once in awhile. The family likes it and it is cheap cheap cheap to make.
Let me know if you're interested in the recipe.