Heat oil in large skillet on medium-high heat. Add onion and bell peppers; cook and stir 5 minutes or until tender. Set aside. Mix ground beef and Seasoning Mix in large bowl until well blended. Shape into 6 patties.
Grill, broil or cook in nonstick skillet on medium heat 5 minutes per side or until burgers are cooked through (internal temperature of 160°F).
Serve burgers on rolls topped with onion and bell pepper mixture. Serve with desired toppings.