Heat oil in a large nonstick skillet over medium-high until shimmering. Season salmon fillets evenly with pepper and kosher salt, and place in skillet. Cook until golden brown on both sides and almost cooked through (an instant-read thermometer inserted into thickest portion of salmon should register 130°F), about 7 minutes total. Remove skillet from heat; transfer salmon to a plate. Let skillet cool slightly, about 2 minutes.
While salmon cooks, zest orange to yield 1 teaspoon grated zest; set aside. Cut orange in half; slice 1 portion into half-moons. Reserve remaining orange half for another use.
After skillet cools slightly, wipe clean and add bourbon, honey, brown sugar, soy sauce, and orange slices. Bring to a simmer over medium. Cook, stirring often, until slightly thickened, about 2 minutes. Return salmon to skillet; spoon bourbon mixture over salmon until fillets are coated and sauce is thickened, about 1 minute. Remove from heat; add butter to sauce in skillet. Gently swirl until butter is melted and combines with the sauce. Serve salmon with sauce, and top with chives and reserved orange zest. Garnish with flaky sea salt.
