Set oven rack about 6 inches from the heat source and preheat the oven's broiler.

Split French bread lengthwise and tear out the soft bread from interior of loaf to hollow out; reserve bread pieces for another use.

Heat a skillet over medium-high heat. Cook and stir beef and celery in the hot skillet until beef is browned and crumbly, 5 to 7 minutes; drain and discard grease.

Stir sour cream and soup mix into beef mixture; cook until heated through, about 3 minutes. Fill prepared bread with mixture; lay tomato slices over meat, sprinkle evenly with cheese blend, and place filled bread on a baking sheet.

Broil until cheese is melted and bubbly, about 3 minutes.