Recipe courtesy of Everyday Food from the Kitchens of Martha Stewart
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In a large skillet, heat the oil over medium-high heat. Add the onion, bell pepper, celery, and garlic; season with salt and pepper. Cook, stirring frequently, until the vegetables are softened, 5 to 7 minutes.
Add the ground beef to the skillet.
Cook, breaking up the meat with a wooden spoon, until it is no longer pink, 6 to 8 minutes.
Stir the tomato sauce, ketchup, and Worcestershire sauce into the beef mixture in the skillet. Simmer until thickened, stirring occasionally, 6 to 8 minutes.
Season the mixture with more salt and pepper, as desired. Spoon onto the buns, and serve immediately.
Sloppy Joe mixture keeps in the freezer for up to 3 months. Freeze individual portions, then defrost as needed.