Mushroom and Bread Stuffed Peppers

For stuffing:

Preheat oven to 375°F.

Using long serrated knife, cut bottom crust and short ends off bread; discard. Cut remaining bread with crust into 1-inch cubes (about 10 cups loosely packed). Place cubes in large bowl. Add oil, thyme, and garlic; toss to coat. Spread cubes out on large rimmed baking sheet. Sprinkle with salt and pepper. Bake until golden and slightly crunchy, stirring occasionally, about 20 minutes. Return cubes to same large bowl.

Melt butter in large skillet over medium-high heat. Add onion, celery, and mushrooms. Sauté until vegetables are soft, about 10 minutes; add parsley. Stir vegetable mixture into bread cubes. Season with salt and pepper to taste. Set aside.

For peppers:

Bring 6 quarts water to boil in large stockpot or Dutch oven over high heat. Add 1 tablespoon salt and bell peppers. Cook until peppers (and tops if using) until they just begin to soften, about 3 minutes. Using slotted spoon, remove peppers from pot, drain off excess water, and place peppers cut-sides up on paper towels.

Adjust oven rack to middle position and heat oven to 350 degrees.