In a large skillet, heat oil at medium-high heat. Add mushrooms, bell pepper, onion and garlic. Cook, stirring often, for about 5 minutes or until liquid of mushrooms have evaporated.
Add ground beef, chili seasoning, salt and pepper. Cook, stirring, 2 to 3 minutes or until beef is not pink anymore. Add tomatoes, tomato paste and sugar, bring to boil smashing the tomatoes with a potato-masher. Reduce the heat and let simmer, uncovered, for about 12 minutes or until preparation has thicken.
Meanwhile, toast kaiser bread. Put mushroom preparation on bottom of inferior kaiser. Cover with swiss cheese and the top of the kaiser.