Clean grill grates and spray with non-stick cooking spray.
Add all ingredients to a large glass bowl and combine thoroughly. Make sure both types of meat and all seasonings are completely incorporated throughout the mixture.
Divide meat mixture into 8 equal parts and shape each part into ¾ inch thick patties. Place patties on a lined tray and use your thumb to create an indent in the middle to keep them from puffing up while cooking.
Cook patties over direct, high heat on your grill for 8 – 10 minutes. Final cooking time will depend on desired level of doneness and how thick you make each patty.
If topping with soft, sliced cheese, add slices about one minute before cooking is complete. If using a harder, chunky cheese, such as blue cheese, move burgers to indirect heat 2-3 minutes before they are done. Top with blue cheese and close lid to allow cheese to melt completely.
Serve on toasted buns with lettuce, tomato, slices of avocado and bacon, if desired – or top with your favorite condiments, instead.