For the garlic noodles: Bring a large pot of water to a boil with the 4 halved garlic cloves. Cook the noodles according to the package directions and drain well. Discard the garlic
Melt the butter with the scallions, ginger and 5 cloves finely chopped garlic in a large skillet over medium heat. Add the flour and cook, whisking, until the flour turns light brown, about 3 minutes. Slowly pour in 1 1/2 cups water and stir until a loose gravy consistency; add up to a 1/2 cup more water if necessary. Add the Parmesan and stir to combine. Add the noodles to the sauce and toss to coat well. Add the cilantro and transfer to a serving platter.
For the roasted cracked crab: Preheat the oven to 375 degrees F.
Melt the butter in a small saucepan with the garlic, fish sauce, oyster sauce, light brown sugar, seasoning sauce, lemon juice and some salt and pepper, stirring to dissolve the sugar. Let cook over medium heat for 5 minutes. Remove from the heat and pour over the cracked crab in a baking dish, tossing to coat. Roast until heated through, about 10 minutes. Serve over the garlic noodles with some roasting juices on the side for dipping.