Preheat your oven to 375 F and grease a muffin tin (12-count). Set aside.
Remove the stems from your mushrooms and give the stems a light chop. Set aside.
In a large saute pan over medium heat, heat 1 tablespoon of olive oil and add the sausage.
Sprinkle with salt and pepper and cook for 6-8 minutes or until sausage is cooked through.
Add the onion, reserved mushroom stems and red bell pepper and saute until tender, about 5 minutes.
Add the garlic and saute for another minute. At this point, add the chicken broth into the pan to deglaze it and scrape any bits off the bottom of the pan.
Bring the mixture to a boil then reduce to a simmer until the liquid is almost gone; about 5 minutes.
Transfer the mixture to a large bowl and let it cool for 10-15 minutes. Add the cubed bread and 1 egg. Toss to combine thoroughly. Gently fold in the mozzarella cheese cubes.
Add the thyme and sage and season with a dash of salt and pepper. Set aside.
Place you cleaned, stem-less mushrooms into each mold of the muffin tin, with the opening facing up.
Drizzle with the remaining olive oil and scoop about a tablespoon or two of the mixture into each mushroom.
Sprinkle the tops with panko bread crumbs and give another drizzle of olive oil over each mushroom.
Bake at 375 F for 20-25 minutes or until the tops are just starting to brown. Remove from the oven and let mushrooms cool for 2-3 minutes and then serve!