In a large heavy bottomed skillet, saute onion in olive oil until soft, about 5 minutes.
Meanwhile, combine millet and water in a small saucepan. Bring to a boil and simmer uncovered for 10-12 minutes or until the millet is cooked and chewy.
Remove stems from the mushroom caps and dice. Set aside the caps for later.
Add the diced stems, garlic and black pepper to the skillet. Saute until the liquid from the mushrooms evaporates.
Preheat oven to 400°F.
Pour the millet, with any remaining water, into the skillet. Add the diced clams with their juice.
Stir in fresh minced parsley and let simmer until the mixture is thick and water is absorbed. Stir in Parmesan cheese.
Place mushroom caps on a parchment lined baking sheet. Divide the filling into 2 portions and stuff the mushrooms. Top mushrooms with 2 TBS cheese each.
Bake in the preheated oven for 20 minutes or until the cheese is golden brown and the mushroom is softened.
Serve with a side salad.
Recipe by Alison's Allspice at https://www.alisonsallspice.com/clam-millet-stuffed-mushrooms/