Heat oven to 400° F. If you have a rice cooker, use that to make quinoa following rice cooker instructions. Otherwise, using a large saucepan, combine the quinoa and 1 cup water (or vegetable broth) and bring to a boil. Reduce heat to medium-low, cover, and simmer until the quinoa is tender and the water is absorbed, 12 to 15 minutes.
If you have a rice cooker, use that to make lentils following rice cooker instructions. Otherwise, using a large saucepan, combine the lentils and 2 2/3 cup water (or vegetable broth) and bring to a boil. Reduce heat to medium-low, cover, and simmer 15 minutes. Add salt and pepper to taste and continue to simmer the mixture, covered, for 3 to 5 minutes, or until the lentils are just tender. Taste to confirm they are done cooking and drain.
While quinoa cooks, cut the zucchini in half lengthwise. Place squash in a colander and sprinkle with 2 teaspoon kosher salt on the cut faces. Set over a bowl or in sink and let drain at least 1 hour, then pat dry with paper towels. Gently scoop out the seeds leaving 1/4-inch thick shell. Arrange in a large baking dish, cut-side up. Season with salt and pepper. Drizzle a teaspoon of olive oil into each zucchini half.
Chop removed zucchini and set aside.
In a large heavy bottom pan, heat 2 tablespoons oil and 4 tablespoons vegan butter. Add onions and cook over medium heat stirring until golden, about 5 minutes.
Add celery, carrots, garlic, and chopped zucchini. Cook 5 minutes more until vegetables are soft and fragrant. Remove from heat.
Stir in cubed bread, cooked quinoa, lentils, flax eggs, nutritional yeast, almonds, olives, and fresh herbs. Add as much vegetable stock as needed to get a moist stuffing that holds together. It should be pretty moist as it will dry when it bakes.
Spoon the mixture into the zucchini, pressing to form a solid mound. Sprinkle with paprika and season with several grinds of black pepper and pinches of salt. Cover with foil and bake until the zucchini is tender, 25 to 30 minutes. Remove the foil and bake until golden, 8 to 10 minutes.