Cook onions in coconut oil over medium heat for 20 minutes. Cover the pan and stir every five minutes.
Meanwhile, in a large bowl, combine the mustard, eggs, cream, and Gruyere. Set aside a tablespoon or so of Gruyere to sprinkle on the top.
Lie the bacon in a pile, one on top of the other. With a serrated knife, cut them in 1/2″ pieces. Cook the bacon with the onions for the last five minutes.
In a pie dish, place half of the onion and bacon mixture. Using a spoon, spread it evenly on the bottom of the dish. Then, pour the egg mixture. Top with remaining bacon mixture, pushing it a bit into the egg.
Sprinkle top with remaining cheese, a couple pinches of nutmeg, salt, and pepper.
Bake for 35-40 minutes or until top is golden brown.