Prep the aromatics. Finely mince half the onion and half the green pepper for the meatballs. Slice the remaining onion and pepper into thin strips for sautéing later. If using mushrooms, slice them now.

Make the meatball mix. In a large bowl, combine ground beef, minced onion and pepper, egg, almond flour, Worcestershire sauce, garlic, 1 teaspoon salt, and 1/2 teaspoon black pepper. Mix gently with your hands until just combined. Don’t overmix or the meatballs can turn dense.

Form the meatballs. Roll into golf ball–sized portions (about 1.5 inches). You should get 18–22 meatballs. Place them on a plate or sheet pan.

Sauté the veggies. Heat 1 tablespoon oil in a large skillet over medium heat. Add sliced onion and peppers (and mushrooms, if using). Season with a pinch of salt and cook 6–8 minutes until softened and lightly browned. Transfer to a plate and keep warm.

Brown the meatballs. In the same skillet, add the remaining oil. Add meatballs in a single layer without crowding. Brown on all sides, about 6–8 minutes total. Work in batches if needed. They don’t need to be fully cooked yet.

Finish in the oven (recommended). Transfer browned meatballs to a parchment-lined sheet pan and bake at 375°F (190°C) for 8–10 minutes, or until they reach an internal temperature of 160°F (71°C). If you prefer, you can simmer them covered on low for 8–10 minutes, but baking keeps them crisp.

Make the cheese sauce. While the meatballs finish, return the skillet to medium-low heat. Add heavy cream and cream cheese, whisking until smooth and slightly thickened, 3–4 minutes. Stir in shredded or torn provolone/mozzarella until melted. If the sauce is too thick, whisk in beef broth, a splash at a time. Season with salt, pepper, and a pinch of red pepper flakes if you like heat.

Combine and melt. Add the meatballs back to the skillet, spoon the sautéed peppers and onions over the top, and gently coat with the cheese sauce. If using sliced provolone, lay slices over the meatballs and cover the pan for 1–2 minutes to melt.

Serve. Spoon meatballs and sauce into bowls or onto plates. Garnish with chopped parsley if you want a fresh touch. They’re great on their own, over cauliflower rice, or with a side salad.