Preheat your oven to 375°F (190°C).
In a mixing bowl, combine the lean ground beef, egg, rolled oats, finely chopped onion, minced garlic, and tomato paste. Season lightly with salt and pepper if desired.
Mix all the ingredients until just combined, being careful not to overmix to maintain a tender texture.
Shape the mixture into a compact loaf and place it on a lightly greased baking pan or ovenproof skillet.
Bake in the preheated oven for 25-30 minutes, or until the meatloaf is cooked through and reaches an internal temperature of 160°F (71°C).
While the meatloaf is baking, prepare the savory gravy. In a small saucepan over medium heat, combine the sliced mushrooms and a splash of water or a little broth to soften.
Once the mushrooms have softened, sprinkle in the whole wheat flour, stirring well to coat the mushrooms. Gradually whisk in the low sodium beef broth to create a smooth consistency.
Let the gravy simmer for 3-5 minutes until it thickens slightly, then season with salt and pepper to taste.
Remove the meatloaf from the oven and allow it to rest for a few minutes before slicing.
Serve slices of meatloaf topped with a drizzle of the warm mushroom gravy. Enjoy your comforting, hearty meal!