Preheat oven to 350 degrees. In a pot, bring 1 ½ cups of water to a boil with the quinoa, a pinch of salt, and stock concentrate. Bring to a boil, reduce to a simmer, and cook for 15 minutes, until softened. Drain and set aside.
Finely chop the shallot. Mince the garlic. Finely chop the parsley. Slice the mushrooms. Halve the bell peppers lengthwise and remove the core, seeds, and white veins.
Drizzle the peppers with olive oil and season with salt and pepper. Roast for about 6 minutes, until slightly softened.
Heat 1 tablespoon oil in a pan over medium-high heat. Add the mushrooms and cook, tossing, for 4 minutes, until golden brown. Add the shallot and garlic and cook for about 30 seconds, until fragrant.
Add 1 tablespoon vinegar, soy sauce, quinoa, and half the parsley. Toss to combine. Cook for another minute or two.
Spoon the quinoa into the peppers and bake for about 5 minutes, until peppers are softened. Serve the peppers and crumble the goat cheese on top. Finish with a sprinkle of remaining parsley.