Preheat oven to 350 °F. Clean and cut zucchinis in half lengthwise. Spoon out all the seeds forming a cavity. Place zucchinis in 13x8 casserole dish and bake for 10 minutes or until zucchinis are soft.
While zucchinis are baking, sauté butter, onions, mushrooms, and all the peppers together for about 7-10 minutes in a large pan on medium heat or until all vegetables are soft.
Add ground beef, salt, garlic, Worcestershire and black pepper to the skillet. Cook until all meat is browned and cooked through.
Remove zucchinis from oven and fill them with the cooked meat mixture. Top with provolone cheese and bake in oven until cheese is all melted. This will take only a few minutes.