Preheat oven to 220 degrees C. Grease a rimmed 32cm x 45cm baking tray with cooking spray.
Whisk 1 tablespoon olive oil, honey, 1 teaspoon salt, 1 teaspoon sage and 1/2 teaspoon pepper in a bowl.
Place pork fillet on the prepared baking tray; rub honey mixture onto pork.
Mix pumpkin, apples and onion in a bowl; drizzle with remaining 2 tablespoons olive oil, 1 teaspoon salt, 1 teaspoon sage and 1/2 teaspoon pepper; toss until well coated. Place around pork fillet.
Bake in the preheated oven until vegetables are tender and pork is cooked, 30 to 35 minutes; baste pork with honey mixture several times during roasting. An instant-read thermometer inserted into the centre of the pork should read at least 63 degrees C.