Cheesy Mushroom Toast

Name: Cheesy Mushroom Toast
Ingredients: 1 loaf French bread*; 2 c. baby portabella mushrooms, sliced; 3 cloves garlic, minced; 3 T. butter (divided); 1/2 c. provolone cheese, grated; 1/2 c. mozzarella cheese, grated; 1/2 c. parmesan cheese, grated; 1/2 c. Swiss cheese, grated; 1/2 c. mayonnaise; 1/2 c. sour cream; 1/4 cup butter, softened; 1 T. dehydrated onion flakes; 1/4 tsp. salt; 1/4 tsp. pepper; 1/4 c. green onions, sliced