Preheat the oven to 350°F. Season the chuck roast on all sides with garlic salt and black pepper to your taste. In a large dutch oven sear the roast in olive oil on all sides over medium high heat.
While the roast is searing slice the peppers into 1 inch slices and slice the onion into wedges. Set aside while you prepare the sauce.
Sweet and Sour Sauce: In a small mixing bowl,whisk together, the tomato sauce, pineapple preserves, brown sugar, rice wine vinegar, Dijon and seasonings. (Start with 1/2 teaspoon of Chinese five spice, and add up to 1 tsp to your taste.) Whisk together until well blended. Reserve the cornstarch for thickening the sauce at the end.
Center the chuck roast in the dutch oven or transfer to a baking dish. Arrange the carrots around the edges. Drizzle the roast with 3 tablespoons of soy sauce.
Arrange the peppers and onions on top of the roast. Season the veggies with a sprinkle of garlic salt and black pepper to your taste.
Pour sauce over the roast and veggies, and cover. Transfer to the oven and bake for 3 hours. (Adjust the cooking time depending on the weight of the chuck roast.)
Check the roast for tenderness with a fork. Use a slotted spoon to remove the roast and vegetables from the dutch oven to a serving platter. Cover and keep warm while you thicken the sauce.
To thicken the sauce place the dutch oven back onto the stovetop and bring the liquid to a boil over medium-high heat.
Dissolve 2-3 tablespoons of cornstarch in a small amount of cold water in a small bowl. Whisk this into the hot liquid. Depending on the amount of liquid, you may need more or less cornstarch. Once the liquid has thickened to your satisfaction remove from the heat.
Carve the roast and arrange on a serving platter with the carrots, peppers and onions. Smother with the sweet and sour sauce and serve with rice or mashed potatoes.
Slow Cooker: Brown the roast on the stovetop per the recipe then arrange in an oval 6-quart slow cooker per the recipe instructions.Cover and cook for 8-10 hours on low. Thicken the sauce on the stovetop per the recipe instructions at the end of slow cooking.