- Cook macaroni in boiling salted water until tender, yet firm. Drain.
- Melt butter in saucepan; blend in flour. Add 1-3/4 cups water and soy sauce all at once; stir until well blended. Simmer until sauce thickens, stirring constantly.
- Remove from heat and blend in pepper and 3/4 of cheese.
- Combine tuna, macaroni and green pepper in ungreased 1-1/2-quart baking dish. Stir in cheese sauce. Sprinkle remaining cheese over top.
- Bake in 425°F. oven until top is golden brown, about 15 minutes.