Cook the Quinoa: Bring the vegetable broth to a boil in a medium saucepan. Add the rinsed quinoa, cover, and reduce the heat to a low simmer. Cook for 15minutes, then remove from the heat and let it steam, covered, for 5 minutes.Fluff with a fork and let cool slightly.
Blend the Pesto: In a food processor, combine the basil leaves, minced garlic, toasted pine nuts, and Parmesan cheese. Pulse until finely chopped, then stream in the ¼ cup of olive oil while blending until smooth.
Hollow the Vegetables: Slice the tops off the beefsteak tomatoes and gently scoop out the inner pulp and seeds with a spoon (save the tomato cores for a vinaigrette or soup). Slice the zucchini in half lengthwise—or horizontally if using round zucchini—and scoop out the center flesh, leaving a sturdy ⅓-inch border to create boats.
Prep the Shells: Preheat your oven to 375°F. Arrange the hollowed tomatoes and zucchini in a baking dish. Lightly brush the insides and tops of the vegetables with the remaining 2 tablespoons of olive oil.
Mix the Filling: In a large mixing bowl, toss the cooked quinoa with ⅓ cup of the fresh pesto until the grains are evenly coated. Fold in a generous pinch of salt and freshly ground black pepper.
Stuff and Top: Spoon the pesto-quinoa mixture into the hollowed tomato and zucchini shells, packing them lightly. Sprinkle the crumbled goat cheese or mozzarella evenly across the top of each stuffed vegetable.
Bake and Serve: Bake for 20 to 25 minutes until the vegetables are tender, and the cheese is melted and golden. Serve immediately while hot, or let cool and serve at room temperature.