Combine the sauce ingredients in a small bowl. Cover and refrigerate until ready to serve.
Heat the olive oil to a 10-inch skillet over MEDIUM heat. Add the diced onions and cook, stirring occasionally, until tender and golden brown. Remove from the heat and set aside to cool.
Add the ground beef to a large bowl and add the parsley, 4 teaspoons Ranch seasoning, pepper, and the slightly cooled onions. Mix well. Divide the mixture into 6 equal portions and form balls. Flatten the balls into ½-inch patties and use your fingers to form a slight depression in the center of each patty. (They will thicken a bit as they cook and shrink a little in diameter).
Coat both sides of the patties with nonstick cooking spray (I used avocado oil spray) or alternately, oil the grates on your grill.
Grill the burgers, covered, until nicely browned on the first side, 2 to 4 minutes. Flip burgers and continue cooking for a few minutes more until the internal temperature reads at least 160 degrees F. Top each patty with cheese, cover and continue to cook just until the cheese melts. If preferred, the burgers can be cooked in a large nonstick skillet over MEDIUM heat.
Serve on buns with lettuce, tomato, and the Smoky Ranch Burger Sauce.