Meanwhile, in a large saucepan, melt the butter and olive oil over medium0low heat. Add the garlic and saute for 1 minute. Be careful, the garlic burns easily! Add the shrimp, salt, and pepper, and saute until the shrimp have just turned pink, about 5 minutes, stirring often. Remove from heat; add parsley, lemon zet, lemon juice,lemon slices, and red pepper flakes. Toss to combine.