Preheat the oven to 350 degrees F (175 degrees C).
Heat oil in a nonstick skillet over medium heat. Add turkey; saute until browned and crumbly, 5 to 7 minutes. Add tomatoes, onion, and garlic. Add couscous flavor packet and cumin; season with salt and pepper. Add couscous; stir and cover. Reduce heat and simmer until couscous is tender, 5 to 10 minutes.
Mix tomato sauce, ketchup, Worcestershire sauce, and hot sauce together in a bowl. Season sauce with salt and pepper.
Bring a large pot of lightly salted water to a boil. Add green bell peppers, red bell peppers, and yellow bell peppers. Cook uncovered until slightly tender, 3 to 4 minutes. Drain in a colander and rinse under cold water for several minutes to stop the cooking process. Drain; shake to dry. Sprinkle salt and pepper inside peppers.
Place a small amount of feta cheese in the bottom of each bell pepper. Fill each pepper halfway with the turkey-couscous mixture; add more feta and fill to the top with more couscous. Cover top with more feta; spoon sauce on top. Place peppers in an oven-proof baking dish.
Bake in the preheated oven until tops are browned, about 20 minutes.