Cook sausage according to package directions. Cool slightly; cut into 1/4-inch slices.
In a greased 13-inch x 9-inch baking dish, layer half the English muffin cubes and half the sausage. Repeat layers.
Drizzle with butter. Sprinkle with the cheese, onion and red pepper.
In a large bowl, combine the eggs, milk, salt and pepper. Pour over casserole. Top with bacon.
Cover and refrigerate overnight.
Remove from the refrigerator 30 minutes before baking. Uncover and bake at 350°F for 45 to 50 minutes, or until a knife inserted into the center comes out clean.
Let stand 5 minutes before serving.