Drain garbanzo beans and black beans separately (starting with garbanzo because you will mash these 1st)
Let each drain in colander well for a few minutes.
Transfer all beans to a clean kitchen towel and dry them well. Let them sit and dry on the towel while you cook the onion.
Sauté diced onion on medium heat, about 6-8 mins. in about 1/2 Tbsp olive oil or butter until tender. Remove from pan and let cool.
Mash garbanzo beans in a small bowl with potato masher or fork till about 70% mashed.
Now mash black beans in medium mixing bowl you will make your burger mix in. Leave some black beans whole, so do not over mash.
Add onion, flour, garbanzo beans, eggs and spices with Worcestershire to bean bowl. If you're adding cilantro and/or adobo do that now as well. Stir mixture and let chill in the fridge for 10-15 minutes.
Scoop 1/3 cup of mixture and form a patty with hands about 1/2 " thick. Repeat till mixture gone.
Heat butter or oil on griddle or skillet at medium heat. Once ready cook patties 4-5 minutes on first side (until browned and solid to flip). Flip patties, cook another 4-5 minutes and on last 1-2 minutes add cheese slice if desired. Once cheese is melted transfer patties to a plate or sheet pan and keep warm in oven till ready to serve.
It's better to serve these immediately if possible. Add all your favorite burger toppings and enjoy!