Preheat oven to 350°F. Melt 1 1/2 tablespoons butter in heavy large skillet over medium-high heat. Add bell pepper to skillet and saute until just tender, about 4 minutes. Mix in green onions; saute 1 minute longer. Remove from heat. Spread 1 1/2 tablespoons butter thinly on bread. Cut bread into 1/2-inch pieces. Layer half of bread in 8 x 8 x 2-inch glass baking dish. Cover with half of cheese, then half of bell pepper mixture. Repeat layering with bread, cheese and bell pepper mixture. Beat milk, eggs, Dijon mustard, dry mustard, salt and pepper in medium bowl to blend. Pour over strata. Bake strata until lightly browned on top and set in center, about 45 minutes. Let stand 10 minutes; cut into squares.