Cut your sausage into two inch segments and cut each segment in half lengthwise. Place these in a large skillet over medium high heat and cook, turning as needed, until lightly browned on both sides.
Slice bread open lengthwise and lay open on baking sheet. Spread one side with mayo and one side with mustard. Arrange 5 cheese slices over bread. Top one side of bread with sauerkraut and pepper slices. Place browned keilbasa slices on bottom half of bread loaf.
Place in oven at 350 for 10-15 minutes, or until cheese is melted and bread is toasted. Remove from oven. Close sandwich and cut into four smaller sandwiches. Serve warm with kettle potato chips or a nice bowl of white beans.