Adjust oven rack to lowest position, turn on convection, and heat oven to 450°F. Combine butter, chives, garlic, 1/8 teaspoon salt, and 1/8 teaspoon pepper in bowl; set aside for serving.
Toss green beans with 1 1/2 teaspoons oil, 1/8 teaspoon salt, and 1/8 teaspoon pepper in separate bowl. Line rimmed baking sheet with aluminum foil and spray with vegetable oil spray. Arrange beans lengthwise across center of prepared sheet, leaving room on either side for potatoes.
Toss potatoes with remaining 1 tablespoon oil, 1/4 teaspoon salt, and 1/8 teaspoon pepper in now-empty bowl. Place potatoes, cut side down, on either side of green beans.
Pat pork dry with paper towels, season with remaining 1/8 teaspoon pepper, and brush thoroughly with hoisin sauce. Lay tenderloin lengthwise on top of green beans. Roast until pork registers 145°F, about 25 minutes.
Remove sheet from oven and transfer tenderloin to cutting board. Dot tenderloin with 1 tablespoon chive butter, tent loosely with aluminum foil, and let rest while vegetables finish cooking.
Gently stir vegetables on sheet to combine and continue to roast until tender and golden, 5 to 10 minutes longer.
Remove sheet from oven, add remaining 1 tablespoon butter to vegetables, and toss to coat. Cut pork into 1/2-inch-thick slices and serve with vegetables.
