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 cool slightly.
02 - In a mixing bowl, blend ground turkey, onion, garlic, parsley, Dijon mustard, salt, and pepper until just combined. Shape mixture into four equal patties.
03 - Heat olive oil in a skillet over medium heat. Cook patties 5 to 6 minutes per side until golden brown and internal temperature reaches 165°F. Transfer to a plate.
04 - Optional: Melt butter in the skillet over medium heat. Toast buns, cut side down, until lightly golden.
05 - Layer lettuce on bottom bun halves. Place a turkey patty atop each, followed by Brie slices, a spoonful of cranberry sauce, and red onion slices if desired. Cover with top buns.
06 - Serve immediately while warm and the Brie is melted.