- Place the zucchini slices in a colander and sprinkle with salt. Let them sit for about 15 minutes to draw out excess moisture. Rinse and pat dry with paper towels. 
- In a skillet over medium heat, add olive oil. Once hot, add the zucchini slices and sauté for about 5-7 minutes until they are tender and slightly golden. Remove from heat and set aside. 
- Preheat a separate skillet or griddle over medium heat. Butter one side of each slice of bread. 
- On the unbuttered side of four slices, layer the cheddar cheese, sautéed zucchini, mozzarella cheese, garlic powder, and black pepper. Top with the remaining bread slices, buttered side up. 
- Grill the sandwiches for about 3-4 minutes on each side, or until the bread is golden brown and the cheese is melted. 
- Remove from the skillet, slice in half, and serve warm.