Combine ground beef, onions, garlic, parsley, sage, mustard, egg, almond flour, pink salt, and pepper in mixing bowl until well combined
Form mixture into 6 thins patties
Slice the avocado half into 3 equal slices
Place one avocado slice on 3 of the patties
Place 1 tablespoon Spicy Mayo into the center of the avocado slices
Cover with a second meat patty and pinch the edges to seal patties together
Grill over medium-high heat for about 5 minutes per side