In a large stockpot, boil jumbo shells in salted water for about 15 minutes; drain & rinse under under cold water. While pasta is cooking, stir-fry ground beef & drain on a paper towels; set aside. Add oil & butter to saucepan & saute garlic, onions, mushrooms for about 2-3 minutes. Add chopped red peppers & sun-dried tomatoes; cook another 2-3 minutes.