Preheat the oven to 375 degrees F. Place bread cubes on a baking sheet and bake them for 8 to 10 minutes, just until they are firm and almost stale, but not too brown.
Heat a large skillet over medium-low heat and add butter and olive oil. Add in the shallots and mushrooms and stir to coat. Cook, stirring occasionally, until the mushrooms soften, about 6 to 8 minutes. Add in 3/4 cup of the stock and bring the mixture to a simmer. Stir in the garlic and cook for 30 seconds, then turn off the heat. Season the mushrooms with the salt and pepper.
In a baking dish (9×13-inch will work, so will something slightly smaller), toss the bread cubes, quinoa and mushroom mixture together. Stir in the sage, parsley and thyme. Drizzle the remaining stock over top evenly, adding a bit more if the bread looks very dry. I like my stuffing a bit crunchy, so if you prefer your’s to be super soft, add more stock. I find that with the salty pretzel bread and the stock, there is no need for more salt. Bake the stuffing for 35 to 40 minutes, until slightly golden on top. Tent it with aluminum foil if it becomes too brown.