Preheat oven to 450 degrees. Chop carrots, celery, onion and panko and egg white in a food processor until fully combined. Transfer to a bowl. Add beef, salt and pepper.
Form mixture into a loaf on a baking sheet. Brush with barbecue sauce. Bake 25 to 30 minutes or until loaf is 160 degrees in the middle. Brush with sauce again halfway through.
In a saucepan, boil potatoes until done, 15 to 20 minutes. Drain and return to pan. Mash with buttermilk until creamy. Season with salt and pepper to taste.
Steam green beans until tender in a steamer on the stove or in a glass bowl in the microwave with a little water, covered loosely with parchment paper. About 4 to 6 minute Transfer to a bowl. Toss with 1 tbs olive oil and season with salt and pepper to taste.
Serve meatloaf with mashed potatoes and green beans.