Heat balsamic vinegar in a small skillet over low heat until simmering. Reduce by about half, 10 minutes. Remove from heat and allow to cool.
In a bowl, add diced strawberries and thyme and mix until combined.
Prepare a grill for high heat. Lightly dip both sides of bread slices in melted butter.
Grill bread until browned, about 3 minutes per side.
To build, spread the goat cheese on toasted bread. Add black pepper, salt, and reduced vinegar to the strawberry mixture. Spoon over the goat cheese.