Mix eggs, Parmesan, heavy cream, ground sage, black pepper, and salt together in a bowl and then prep the ham, onions, and bell peppers.
In a 10 inch non-stick frying pan, heat oil and sauté onions, peppers and ham until vegetables are soft. Add extra oil to pan and add egg mixture to pan; cook over medium heat for 2 minutes as eggs begin to set up. Place pan in a 375° oven for 8-9 minutes; remove from oven and let rest. Slide frittata on to serving plate and cut into wedges.