Preheat oven to 250 degrees F. Spread all the spices (chile, coriander, cumin, oregano, peppercorns) on a sheet of aluminum foil with the edges turned up to avoid spillage and toast the spices for a few minutes. Transfer the toasted spices to a molcajete or mortar and pestle and grind together.
Sprinkle the pork cubes with the spices, covering all surfaces of the meat as much as possible. Let the pork sit covered in the refrigerator for 2 hours.
Create a beurre manie by mashing the flour into the butter in a small bowl. Set aside until needed as a thickener for the stew.
Heat the grape seed oil in a deep saute pan over medium-high heat until it begins to shimmer. Add the pork cubes and brown on all sides. Lower heat to medium and add the garlic and onion and stir to combine flavors. Cook until the onion turns translucent, then stir in chili powder and paprika. Add 4 cups water and reduce heat to low. Cover and let simmer until fork tender, about 2 hours. Add water as needed throughout the cooking process. In the last 30 minutes of cooking time, add the beurre manie to thicken. Serve hot.