Heat an outdoor grill or indoor grill pan. Divide the ground beef into four equal portions. Season each generously on both sides with the taco seasoning. Cook the burgers until desired doneness.
Heat the oil in a large nonstick skillet until shimmering. Add the peppers and onions. Season them with oregano and salt and pepper to taste. Cook stirring, until the onions are translucent and the peppers are tender.
Serve the burgers on buns, top with vegetables, salsa, guacamole, chipotle mayo, and/or chopped cilantro.
You can always skip the buns and serve on lettuce leaves instead!