Dice onion finely. Cut jalapeño in half, remove seeds and veins per your individual taste. For spicier burgers, leave more seeds and veins.
Sautee onion and jalapeño in a splash of olive oil until softened.
Add ground beef, soy sauce, salt, pepper, half of the cheese, the cooked jalapeños and onions, and the cilantro. Mix gently until ingredients are distributed.
Divide mixture into patties and cook. I used a griddle, because I had so many to make, but you could just use a pan on the stove top. They would be excellent, grilled.
Cook for approximately 5 minutes on first side until edges start to brown.
Flip burgers and add remaining cheese. Use an instant read thermometer to test for doneness. I cooked my burgers to the USDA recommended 165 degrees. Cheese will melt as burgers cook to their finished temperature
Assemble burgers. Add mayo or sour cream to a fresh brioche bun, then add burger, avocado, tomato, and spring mix.