In a small bowl mash the avocado with the everything bagel seasoning.
Slice the red onion into thin rounds and gather the cleaned baby spinach.
Slice the bagel in half (horizontally) and lightly toast.
Assemble Bagel Sandwich
Shmear the avocado mixture on one side of the bagel. Then layer the red onion and spinach on top.
If you have leftover avocado, shmear on second side and then top with cheese. Put the two halves together, and slice in half. Enjoy!
You can easily add additional veggies to this sandwich. Some others that go well are bean sprouts, thinly sliced radish, thinly sliced cucumbers and roasted red peppers. The cheese is totally optional as well.