Heat oven to 425 degrees.
In a medium size skillet, add butter and olive. Once butter is melted, add onions and celery and cook until onions are clear. Season with salt and pepper. Remove from heat and let cool.
Cut zucchini lengthwise and scoop out seeds. Set aside.
Add herb stuffing, stock, salt, pepper, celery salt, thyme and 1/4 cup of cheese to onions and celery. Mix well.
Place zucchini on a foil lined baking sheet drizzled with olive oil. Sprinkle salt in the well of each zucchini and stuff with dressing mixture. Lightly drizzle each zucchini half with olive oil. Bake in oven for 15 - 18 minutes or until lightly brown on top. Sprinkle with remaining cheese and place back in oven until cheese is melted.