use higher heat. french omelet, which is basically what you are trying to do, is done in a small pan over medium-high heat. add oil or butterto hot pan, let it heat/foam.
add egg and swirl to coat the pan. stir the middle of the egg a few times until it fluffs under the fork (10 seconds at most. add your ingredients, shake once, and fold the omelet over. let it cook over the heat for 5-10 seconds, then slip out onto a plate.
that's it. this is definitely a "trick" but once learned, will serve you well.
also, ingredients cook well in an egg- that fucker gets hot, and stays hot, in there- the secret is to grate and mince the toughest ingredients, and use sparingly- grated onions, peppers and paper thin mushrooms will cook in this method. anyway, you want them slightly crisp, like a good stirfry (same basic idea).
if you really want a hands-on demo, go to a restaurant serving a breakfast bufffet with an omelet station (drop about $15 per person) and watch the cook. a good omelet makeer can do three pans at once and turn out 1 per minute or so. see in it action a few times and you'll get the trick.