Preheat oven to 350°F.
Place mushrooms in a large bowl, pour boiling water over them and let soak.
Meanwhile, heat oil in a large, high-sided skillet or Dutch oven over medium-high heat. Working in batches, brown chicken on all sides, turning occasionally, 4 to 5 minutes. Transfer the chicken to a 9-by-13-inch baking dish.
Reduce heat to medium and add peppers and onion to the pan; cook, stirring often, until soft, about 3 minutes. Stir in fennel; continue cooking, stirring often, until wilted, about 3 minutes.
Add garlic, rosemary, orange zest and thyme; cook, stirring constantly, for 30 seconds. Pour in vinegar and cook for 1 minute, stirring and scraping up any browned bits. Remove from the heat.
Drain the mushrooms in a fine sieve lined with a paper towel; reserve the soaking liquid. Rinse the mushrooms, then coarsely chop. Stir them into the pan along with the soaking liquid, wine, tomato paste and salt. Return to the heat, bring to a simmer, then pour the mixture over the chicken. Cover the baking dish with foil.
Bake the cacciatore until bubbling, about 45 minutes. Let stand for 10 minutes before serving (or follow make-ahead instructions).
Ingredient note: Like fresh mushrooms, dried have a shelf life. When purchasing them, look for whole mushrooms in the package without a lot of powdery dust or spiky shards; the color should be uniformly brown. Porcini can also be purchased online from Oregon Mushrooms at oregonmushrooms.com.