For added moisture and flavor in our turkey burger, we’ve added lightly sautéed shallots and garlic — they were mixed into the ground turkey meat. We also stuffed the patties with cheddar cheese for a rich gooey-centered burger. The combination of oil-coated shallots and garlic makes the turkey patty stick less to the grill, and adds a nice flavor profile to the otherwise bland turkey meat.
In a large skillet, use two tablespoons olive oil to cook shallot and garlic, stirring often for three minutes. Remove from heat. Add cooked shallots and garlic to a bowl with ground turkey. Stir or use hands to combine.
Make eight evenly sized patties. Divide cheddar evenly among four of the patties. Sandwich the other four patties on top. Make sure the two halves are tightly sealed. The cheese will melt inside patties when grilled. Grill turkey patties on moderately high heat for eight-to-nine minutes, turning over once, midway.
Preheat oven to 375 degrees. Cut the onions into ¼-inch rounds. Place in a medium bowl, and toss with balsamic vinegar, olive oil, salt, and pepper. Place on a baking sheet and bake for 10 minutes. Remove from oven, and mix to incorporate cooking liquids.
Place one turkey patty, a quarter portion balsamic onions, and avocado on top of one half of a bun, use other half to sandwich burger. Spread ketchup and mayonnaise, to taste. Repeat steps for remaining three burgers.