Preheat oven to 375 degrees. Prepare your bread pan by spraying with cooking spray (if preferred, use oil or butter).
Place potatoes in a large pot covered with water; bring to a boil and allow to cook uncovered until softened.
While potatoes boil, finely dice onion and mix it with 1/3 cup of the marinara sauce, egg, thyme, salt, and pepper. Add bread crumbs and beef and mix thoroughly (your hands are typically the best utensil for mixing here).
Shape into loaf pan and top with remaining marinara sauce. Bake for 25-30 minutes or until no longer pink inside and a meat thermometer reads 160 degrees.
While meatloaf bakes, assemble the salad: dice bell pepper, slice tomatoes in half, and toss with lettuce. Also make mashed potatoes: drain potatoes, add milk and butter, then mash with a hand-held masher or a mixer if a smoother consistency is desired. Chop the pineapple.
Serve meatloaf with salad, mashed potatoes, and pineapple chunks on the side.