01 - Combine cranberries, sugar, water, orange zest, and salt in a small saucepan. Simmer over medium heat, stirring occasionally, until cranberries burst and sauce thickens, about 8 to 10 minutes. Remove from heat and let cool slightly.
02 - In a bowl, mix ground turkey, onion, garlic, parsley, Dijon mustard, salt, and pepper until just combined. Shape mixture into 4 equal patties.
03 - Heat olive oil in a large skillet over medium heat. Cook patties for 5 to 6 minutes per side until golden brown and internal temperature reaches 165°F. Transfer cooked patties to a plate.
04 - If desired, melt butter in a skillet over medium heat. Toast buns cut side down until golden brown.
05 - Layer lettuce on bottom halves of buns, place turkey patties on top, add Brie slices, spoon cranberry sauce generously, and optionally add sliced red onion. Cover with top buns.
06 - Serve immediately while warm and Brie is melted.