Preheat oven to 350 degrees F (175 degrees C). Line 3 baking sheets with parchment paper.
Mix oyster mushrooms, panko, garlic, black pepper, and salt together in a large bowl with your hands. Mix in ground beef until mixture is sticky and thoroughly combined.
Scoop beef mixture with an ice cream scoop and roll lightly into balls. Place on the lined baking sheets.
Bake in the preheated oven until browned and an instant-read thermometer inserted into the center reads 165 degrees F (74 degrees C), about 20 minutes. Remove from oven and let stand for 10 minutes before serving.
Grind dried parsley into a fine dust using a coffee or spice grinder. Garnish meatballs with parsley dust.
