In a medium saucepan, combine rice, thyme, basil, 1/2 teaspoon salt, and stock or broth. Cover and bring to a boil. Reduce heat; simmer 40 minutes.
Preheat oven to 350F degrees. Wash mushrooms well; slice large mushrooms into thick slices, cut small mushrooms in half.
Melt butter in a large stovetop casserole dish. Add onions; saute until golden brown. Add prepared mushrooms; saute until lightly browned. Season to taste with remaining salt and pepper. Stir in rice mixture and any stock or broth not absorbed.
Cover and bake 15 to 20 minutes. To serve, sprinkle parsley over top.