Savory Overnight French Toast Bake - XO&So: Vegetarian Comfort Food

Name: Savory Overnight French Toast Bake - XO&So: Vegetarian Comfort Food
Cuisine: French, European, Mediterranean
Ingredients: Half (approx. 250 g) of a large loaf of day-old French bread, cubed; 3 eggs; 2 tsp. smooth Dijon mustard; 1/4 tsp. onion powder; 2 tbsp. chives, chopped; 1 cup milk; 3 oz. (a little more than 1/3 cup) of Gruyere, shredded; Salt and pepper