Preheat oven to 425°F.
Heat the vegetable oil in a large ovenproof skillet over medium-high heat,
Add 1 tablespoon oil to pan; swirl to coat. Combine the salt, pepper, garlic powder and thyme in a small bowl, and sprinkle pork with salt, pepper, garlic powder and thyme.
Add pork tenderloin to the skillet and brown on all sides.
Cover skillet with oven safe lid and bake at 425°F for 10 minutes.
Meanwhile, cut bell peppers into strips, sprinkle with salt and pepper, and the garlic and add to the skillet with the pork.
Cook pork and vegetables together, until vegetables are soft, and the pork is cooked (thermometer needs to read 145°F), about 10-15 minutes.
Remove skillet from oven, and remove pork and vegetables to a plate, and keep warm.
Place the skillet on the stove, and heat to medium high.
Sprinkle the surface with the flour and whisk in the chicken stock gradually. Season with salt and pepper and cook until gravy is thickened.
Slice the pork tenderloin and pour gravy over the top.