6 1/2 tablespoons olive oil
10 ounces shiitake mushrooms, stems removed and caps sliced thin, or 1/2 pound regular white mushrooms including the stems, sliced
2 1/4 teaspoons salt
1/4 teaspoon fresh-ground black pepper
1 large onion, chopped
1 quart water
1 quart canned low-sodium chicken broth or homemade stock
1/3 cup long-grain rice
2 pounds asparagus, tough ends snapped off and discarded, spears cut into 1-inch pieces
16 1/2-inch slices baguette
1/4 pound Gruyère, shredded