Place all ingredients except buns in a large bowl and mix gently until just combined. Without compacting the meat too tightly, form 12 patties.
Preheat grill to high. Cook burgers about 6 min. per side or until an instant-read thermometer reaches 160°F (71°C) when inserted into centre of burger. Allow to rest 5 min.
Mix ranch dressing with chopped fresh dill. Dress burger with 1 tbsp of sauce, sliced fresh avocado with a squeeze of lemon juice and a tuft of alfalfa sprouts.