Combine ricotta, parmagiano, yolk, zest and salt in large bowl. Mix well. Sprinkle half of the flour on the mixture, gently turn with spatula a few times to incorporate. Dump mixture on clean, lightly floured countertop. Sprinkle remaining flour on top of the mixture. Gently knead with your fingertips, just bringing together the mixture until flour is incorporated through. This only should take a minute or two. Any longer and you will be over-kneading. *If you are using skim milk ricotta - you may have to use more flour, as there is more water content in skim ricotta.
Divide dough into 4 parts. Take one part and roll into a long, 1″ diameter log. Cut gnocchi into 1″ pieces. You may use the tines of a fork to get those pretty grooves that will eventually disappear after frying anyways.
Heat skillet over medium-high heat. Add butter and olive oil. when butter is just lightly browned, add gnocchi in single layer. Fry on one side for 2 minutes, flip. Add chilli. Fry other side for 1-2 minutes. Timing really depends on how big/thick your gnocchi is. Do a taste test - do you taste flour? Not done yet. Serve with a sprinkling of lemon zest, parmegiano and parsley.