Place the egg yolks in a bowl with the milk and combine. In a separate bowl, whisk the egg whites to medium soft peaks. Gently fold into the egg yolk mixture. Set aside (do not allow to sit for too long).
Spray a small non-stick frying pan with oil spray and place over medium heat. Add the baby spinach and cook for 1-2 minutes or until wilted. Remove from pan and wipe pan clean. Spray pan again and return to the heat.
Pour in the egg mixture and cook for 2-3 minutes or until surface is nearly firm. Place the ham, spinach and cheese over half the omelette, then fold over the other side to enclose the filling. Serve immediately. Repeat ingredients and method for additional omelettes.