Preheat your oven to 375 degrees.
Place your Brie cheese round in the center of your skillet and slice off the center round about 1/4" from the top. Discard rind.
Scatter your sliced onions around the Brie in the skillet. Add salt, pepper and thyme to taste. Add olive oil evenly over the onions and toss.
Place skillet in the oven and bake for 20 minutes or until the cheese is oozy and melted and onions are softened.
In the meantime, prepare your spaghetti and boil according to the package. Drain but reserve a cup of pasta water.
To plate or serve you can do it one of two ways. The first way is a creamier version. Take a small serving of spaghetti and place right in the melted Brie round. Add some peas and ham and mix around then plate with onions. Garnish with red pepper flakes, pepper and chopped parsley.
For a lighter flavor, add ALL the pasta to the skillet (note you can remove the bottom pieces of rind if you choose but it's edible). Add all the ham and peas then add some of your reserved pasta water to thin out and mix everything in the skillet. The reason you need to add the pasta water for this version is because the cheese will congeal very quickly and be hard to mix when you have so many ingredients in the mix. Plate from the skillet and garnish with red pepper flakes, pepper and chopped parsley.