Place butter, garlic, parsley, and lemon juice in a small microwave-proof serving bowl.
Microwave, uncovered, on HIGH (100%) for 1 minute or until butter is melted; set aside.
Arrange clams in a circle on a flat 10-inch microwave-proof plate.
Cover loosely with heavy-duty plastic wrap, leaving enough room for shells to open.
Microwave on HIGH (100%) for 3 to 5 minutes or until shells pop open.
If any clams remain unopened, lift out opened clams; then microwave unopened ones on HIGH (100%) until shells open, checking at 30-second intervals.
Let stand for 1 minute.
Serve in shells, drizzled with garlic butter.