Fill a 1 1/2 qt. pot 2/3 full of water, and bring to a boil over medium-high heat. Add uncooked macaroni from the package and cook 8-10 minutes as directed. Drain pasta and return to pot.
While water boils and macaroni cooks, scoop out the interior of the tomatoes to prepare for stuffing. Do this by carefully cutting a large hole in the top of each tomato and then scooping out the flesh and seeds with a grapefruit spoon.
Preheat broiler to high.
When macaroni is done, stir in butter and chili powder into the noodles until butter has melted. Then, stir in cheese powder packet and milk until powder is incorporated. Stir in black beans.
Scoop macaroni and beans into each hollow tomato. Pile a couple tablespoons of cheddar cheese on top of each one. Place stuffed tomatoes on a foil-lined baking sheet, and broil for 7-10 minutes or until cheese on top is melted and starting to brown. Serve right away.