1. Preheat a skillet over medium heat so it is hot enough to create a golden crust.

2. In a small bowl, mash the ripe avocado with a fork until smooth. Season with salt and pepper to taste.

3. In another bowl, mix the shredded mozzarella and cheddar cheese together until evenly combined.

4. Spread butter on one side of each slice of bread. On the opposite side of two slices, spread a thin layer of mayonnaise.

5. Place the bread slices with the mayonnaise side facing down into the skillet.

6. Spread the mashed avocado evenly over the bread in the skillet, then sprinkle garlic powder and onion powder on top.

7. Add the cheese mixture evenly over the avocado layer. If using, place fresh basil leaves on top.

8. Place the remaining slices of bread on top, making sure the buttered side is facing outward.

9. Grill the sandwiches for about 3–4 minutes per side until the bread is golden brown and the cheese is fully melted. Adjust heat if needed to prevent burning.

10. Remove from the skillet, let cool slightly before slicing, then serve warm.