• In a large bowl, mix all meatball ingredients with your hands (except the oil) until just combined.
• Using a cookie scoop, shape the mixture into 1 & 1/2-inch balls (about 2 tablespoons each) rolling briefly between the palms of your hands.
• Place on a clean platter, cover and refrigerate for about 30 minutes, if possible - this helps them retain their round shape when cooking.
• In a large nonstick skillet, warm the olive oil over medium-high heat until shimmering. Working in batches to avoid crowding, add the meatballs and cook turning continuously until browned on all sides, about 5-6 minutes (reducing the heat if they're browning too much.) Repeat with the remaining meatballs. Transfer to a plate and cover with foil.
• Reduce the heat to medium and in the same skillet with the drippings, add the butter. Once melted, add in the flour and whisk constantly until combined and no lumps remain.
• Slowly pour in the beef stock, whisking well. Add in the ketchup, Worcestershire, onion powder, whisking to combine; bring to a simmer, then turn down the heat to a gentle bubble and let the sauce thicken, stirring continuously for about 2 minutes. Season with salt and pepper, to taste.
• Add the partially cooked meatballs back to the skillet and nestle into the gravy; cover and cook another 8 to 10 minutes until cooked through (with an internal temperature of 160 degrees F.)

Assemble the Sandwiches

• Slice open the hoagie rolls and place under the broiler on low until they are light golden brown (watch very closely so they don’t burn!) OR just put them in the oven to get crisp and golden.
• Arrange 3 meatballs on one side of each hoagie, top with a handful of shredded cheese, broil (or bake) on low until the cheese is melty.
• Garnish with a little finely chopped fresh thyme or parsley and serve immediately.