Combine ground beef, onion, jalapeño, cilantro and 1/4 cup cheese in medium bowl, mixing lightly but thoroughly. Lightly shape into four 1/2-inch thick patties.
Heat large nonstick skillet over medium heat until hot. Place patties in skillet; cook 10 to 12 minutes until instant-read thermometer inserted horizontally into center registers 160°F, turning occasionally. About 3 minutes before burgers are done, top evenly with remaining 1/4 cup cheese.
Place burgers in tortillas or buns; season with salt and black pepper, as desired. Top with desired toppings.