Place an 8 to 10-inch non-stick saute pan over medium heat. Add 1/2 tablespoon olive oil and heat until smoking. Add 1/3 of the egg mixture to the pan and cook the thin frittata until golden brown. Using a heat resistant spatula if necessary, flip the frittata over and cook on the other side. Remove to a plate to cool. Repeat process until the egg mixture is finished, placing each successive frittata on a different plate.
When the frittatas have cooled, stack 1 on top of the other and cut into 1/4-inch julienne strips. In a clean mixing bowl, combine the remaining escarole, the orange zest and segments, the remaining extra-virgin olive oil, lemon juice, and lemon zest. Season, to taste. Combine frittata strips with the escarole salad mixture. Garnish with fennel fronds. Serve immediately.