1Spray 13x9-inch (3-quart) glass baking dish with cooking spray. In 10-inch skillet, melt butter over medium-high heat. Add spinach, bell peppers and leeks; cook 4 to 5 minutes, stirring frequently, until crisp-tender. Remove from heat.
2In baking dish, layer ham, spinach mixture, 1 cup of the Cheddar cheese and the bread. In large bowl, beat eggs, milk, mustard and pepper with wire whisk until blended; pour over bread. Sprinkle with remaining Cheddar cheese and the Italian cheese blend. Cover with foil; refrigerate at least 4 hours but no longer than 24 hours.
3Heat oven to 325°F. Bake loosely covered 40 minutes. Uncover; bake about 30 minutes longer or until top is golden brown and knife inserted in center comes out clean.