Heat oven to 350 degrees.
Butter an 8x8 or similar baking pan or dish.
In a large mixing bowl, add the eggs, Dijon mustard, Herbs de Provence, and diced onion. Whisk to combine.
Add the shredded zucchini then the shredded sweet potatoes, stir in the shredded cheese. Sprinkle the top with the flour and add the salt and pepper. Stir to combine and pour mixture into the buttered baking dish.
Bake uncovered for 40-50 minutes. *If making ahead and refrigerating, add 15 minutes to the baking time and cover the baking dish for the first 15 minutes to prevent the top from getting too brown.