Cook manicotti according to package directions; drain. In a large skillet, cook the beef, onion and green pepper over medium heat until meat is no longer pink; drain. Stir in the tomato sauce, oregano and thyme; bring to a boil. Reduce heat; simmer, uncovered, for 10 minutes. Add 1/2 cup cheese; stir until melted.
Stuff half meat mixture into manicotti shells; arrange in a greased 8-in. square baking dish. Spoon remaining meat mixture over shells.
Bake, uncovered, at 325° for 20 minutes. Sprinkle with remaining cheese; bake 5-10 minutes longer or until heated through and cheese is melted.