Preheat gas or charcoal grill to high heat.

Heat a small amount of olive oil in heavy frying pan.

Crumble Italian sausage into pan and cook about 5 minutes, breaking apart with back of the turner as it cooks.

When sausage is well-browned, remove to bowl. If needed, add a bit more olive oil, then saute onions until they’re starting to soften, about 2 minutes.

Add garlic and continue cooking until onions are starting to brown, a few minutes more.

Add Italian sausage back into pan, then add red pepper flakes and pasta sauce and simmer 2-3 minutes while you chop the spinach.

Add chopped spinach and let it wilt and cook down, stirring so it’s evenly distributed in the sausage/onion mixture.

Turn off heat and stir in ½ cup mozzarella, chopped basil and parsley.

Remove stems from mushrooms caps, being careful not to break the mushrooms. Scrape out brown gills from inside mushrooms if desired.

Brush both sides of mushrooms with olive oil.

Put mushrooms on grilling pan or directly on grill, inside facing down, and cook about 4 minutes, until mushroom is slightly browned and starting to soften.

Remove mushrooms from the grill. (I put them on a wooden cutting board.)

One at a time, stuff the inside of each mushroom with sausage/spinach/cheese mixture, then top each mushroom with about 2 T grated mozzarella.

Carefully put mushrooms back on grilling pan or on the grill, stuffing facing up of course!

Cover grill and cook about 5 minutes, checking often and removing from grill when mushrooms are cooked through, and cheese is melted and starting to brown, and stuffing mixture is hot.

Serve immediately.