Set the oven to heat at 400°F.
Make a lengthwise cut in each chicken breast, careful not to cut through completely, creating a pocket for the filling.
Season the chicken breasts thoroughly with kosher salt, pepper, onion powder, garlic powder, dried oregano, and drizzle with olive oil.
Heat an oven-safe pan over medium-high heat and lightly brown the chicken breasts for about 3 minutes on each side, then remove from heat.
While the chicken cooks, core and thinly slice the apple, then toss the slices with lemon juice to keep them fresh.
Fill each seared chicken breast with apple slices and brie cheese, and secure with toothpicks if needed.
Place the stuffed chicken back in the skillet and bake in the oven for 15 to 20 minutes until the internal temperature reaches 165°F.
Garnish with fresh thyme if you like before serving.