Preheat oven to 350°F. Grease a 13 x 9-inch baking dish; set aside.
Cook noodles in a large pot of well-salted boiling water according to package directions for 1 minute less than al dente. Drain well.
Meanwhile, heat a large skillet or Dutch oven over medium-high heat. Brown beef, bell pepper, and onion in the skillet; drain excess grease. Season with salt and pepper, to taste. Add tomatoes (with juice), crushing the tomatoes slightly with a wooden spoon. Stir in the condensed soup, brown sugar, chili powder, dry mustard, and garlic powder.
Add the cooked noodles to the ground beef mixture; toss to combine.
Transfer to the prepared baking dish. Sprinkle with cheese. Bake, uncovered, for 20 minutes. Add the fried onions on top; return the dish to the oven for about 5-10 more minutes, until the filling is hot and bubbly and the onions are lightly browned on top.