Burgers for 14

Our friends who have a country house Pennsylvania are having so many people over for the weekend of the 4th that D. and I are sleeping in a tent on the lawn. We're planning a BBQ for 14, and I offered to bring burgers. I've been buying all of our meat free-range, local, or organic, so the endeavor was not cheap, but I hope worth the effort. We make a variation of these burgers about once every two weeks, but we never eat them with buns. We have to find a place near us here in Brooklyn that makes good hamburger buns.

Gourmet Free Range Beef Burgers

7 lbs. free range ground sirloin
2 red bell peppers
2 red onions
1 lb of cremini mushrooms
4 eggs
1 1/2 cup panko
salt
pepper
paprika
cumin
tamari
worsteshire sauce
sriracha sauce

Finely chop 2 medium red onions and set aside in a bowl. Do the same with peppers and mushrooms, both in separate bowls. Saute onions until they are soft. Add red peppers and saute until they are soft as well. The onions will be limp and will have lost most of their color. Add the mushrooms and saute until the mushroom have gotten just soft. Set aside in a cool place (put in the fridge after its cooled for a bit). Mix in a bowl the eggs, salt, pepper, paprikia, cumin, tamari, w. sauce, and sriracha to taste. Don't add too much sriracha. Take out the ground sirloin when the veggies have cooled and mix the veggies and spiced egg mixture into the ground sirloin, dump in 1 1/2 cup of panko and work with your hands until the meat is the right consistency for burgers. Shape and either cook 'em up right away, or store them in the fridge or freezer between parchment paper. Best grilled, but you can cook 'em in a cast iron pan. Enjoy!