Place mushrooms into a grill basket or thread onto skewers. (If using bamboo skewers, soak them for 30 minutes in water before using).
Combine the butter, dill and garlic salt. Brush 1/3rd of the mixture over the mushrooms.
Transfer to the grill and grill for 10-15 minutes or until just tender, rotating occasionally and brushing with the remaining dill mixture a few more times.
Notes
Note: I like to double the amount of dill weed and garlic salt.