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1
Heat 1 teaspoon olive oil in a large saucepan over medium heat; cook and stir 1/4 cup onion and 2 garlic cloves in the hot oil until onion is slightly transparent, about 5 minutes. Increase heat to medium-high; add beef broth, tomato sauce, oregano, basil, sugar, parsley, thyme, savory, red pepper flakes, and marjoram. Simmer mixture, stirring occasionally, until flavors have blended, 15 to 20 minutes.
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2
Heat 1 teaspoon olive oil in a large saucepan over medium-high heat; cook and stir 1/4 cup onion and 1 garlic clove in the hot oil until onion is tender and slightly transparent, about 5 minutes. Cook and stir ground beef into onion mixture until browned and crumbly, 10 to 15 minutes. Drain excess grease.
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3
Stir ground beef mixture and green bell pepper into tomato sauce mixture; simmer for 15 minutes.
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4
Preheat oven to 350 degrees F (175 degrees C).
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5
Pour meat sauce, water, mostaccioli, and shredded mozzarella cheese into a 3-quart glass baking dish; stir well. Cover dish with aluminum foil.
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6
Bake in the preheated oven for 20 minutes. Remove aluminum foil and lay mozzarella cheese slices over mostaccioli mixture. Bake until cheese is melted and bubbling, about 10 minutes.
