I could not find yellow lentils. Which of the following would be the best substitute: red lentils or yellow split peas? (Both are listed as subs...

Thanks all - I used the red lentils and recipe came out fine.

I think the yellow split peas are one of the Indian dals, like chana dal or mung dal -- lentils which are split and have the seed coat removed, like the red lentils are. Since the red lentils are yellow when cooked, I'd say that if you have them already, go ahead with them. They cook through quickly, so adjust if necessary.
North American/European yellow split peas take a much longer time to cook.

I think you could use either or even a combination of the two.