Yes, you can definitely have beans and legumes in P1. In fact, you are encouraged to eat them and do so often in P1, as they not only have good carbs that can help you feel less lethargic and more comfortable in P1, but they have lots of fiber that helps keep you from feeling <cough> impacted during P1.

That's a common problem...so if the beans don't take care of it, feel free to add some metamucil capsules or other remedies to keep things moving.
I highly recommend homemade 3 bean salad for a snack and side dish in P1. Not only does it have those beans (which add protein, too!), but it has veggies and good fat...it tends to make you feel full, stay full, and feel much better! Great stuff.