Make It Now:

1. Make the Filling: In a large saute pan, heat oil over medium-high heat until shimmering. Saute bell peppers, onions and mushrooms until they begin to soften, about 4-5 minutes. Stir in garlic and cook about 30-60 more seconds. Season the veggies lightly with salt and pepper and then set aside.
2. Add the ground beef to the same saute pan and cook, breaking it up with a wooden spoon or spatula along the way, until there is no longer any pink showing. While it cooks, season the meat with 1 teaspoon salt, 1/2 teaspoon pepper, and a pinch of red pepper flakes. Drain any excess grease.
3. Stir in Worcestershire sauce and the cooked veggies until everything is combined. (Freezing instructions begin here.) Set filling aside. 
4. Build the Sandwiches:Wipe the saute pan clean. Lay the bread slices on a cutting board and butter one side of each piece of bread. Then lay them butter side down. On the inside of one piece of bread, place a slice of cheese, scoop about 1/3 cup of the beef mixture on top of that, top with another slice of cheese, and place another piece of bread on top (butter side up).
5. Grill the Sandwiches: Place the saute pan over medium heat. Grill each sandwich for 2-3 minutes per side, until the outside is browned and cheese is melted.

Freeze For Later: Follow instructions through Step 3. Place the cooled meat/veggie mixture in a freezer bag and seal. Freeze the meat, cheese slices, and bread together as a meal kit.

Prepare From Frozen: Thaw the meat kit components in the refrigerator overnight. Follow Steps 4-5.