Heat oil in a large, cast-iron pan over medium-high heat. Add diced peppers and onion; sauté for 5 minutes. Push veggies aside and increase heat to high.
Add sausage, plus a pinch of salt and pepper to the center of the pan. Sear until browned, then crumble and cook until fully cooked and golden brown.
Reduce heat to medium-low. Add garlic, oregano, garlic powder, and marinara sauce. Cover and simmer for 5 minutes. Stir in the fresh basil. Taste and adjust seasoning if needed. Depending on marinara sauce used, I typically add 1/2 teaspoon pepper and 1/4 teaspoon salt.
Preheat oven to high broil, positioning the rack in the center. Halve the hoagie buns, spread the insides with softened butter, and lightly sprinkle with garlic powder. Broil until lightly toasted (30–60 seconds). Remove from oven.
Set the top buns aside. Divide the meat sauce evenly among the bottom buns. Sprinkle shredded mozzarella cheese on top of the meat. Broil until the cheese is melted (30–60 seconds). Assemble the sandwiches and enjoy immediately to prevent them from getting soggy.
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Notes
Note 1: I use 1 red and 1 orange pepper, but any color works. Dice peppers and onion into small, uniform pieces for the best sandwich filling. Larger pieces won’t tenderize quickly or blend well with the meat.Note 2: Use mild or spicy sausage based on preference. Any package size close to 1 pound works, including a 19-ounce package. Remove casings from Italian sausages before cooking.Note 3: To soften butter quickly, pour hot water into a glass bowl or cup that fits over the butter. After a few minutes, dump out the water and cover the butter with the warm dish. It should soften nicely in 5–10 minutes. When broiling, watch closely as the sandwiches can go from perfectly toasted to burnt in seconds!Nutrition Note: Nutrition information is for the sandwich filling only, as buns and cheese can vary greatly.Storage: Keep filling in an airtight container in the fridge for 3–5 days.