Heat oven to 400ºF and line a medium baking sheet with parchment paper. Heat olive oil over medium heat in a medium skillet and add onions. Sauté for 5 minutes. Stir in garlic and mushrooms, sauté 5 minutes longer. Cool 5 minutes.
Combine ground beef, mushroom mixture, egg, almond flour, oregano, basil, sea salt and pepper in a medium mixing bowl and use hands to thoroughly combine. Form mixture into an oval loaf shape on the prepared baking sheet. Brush with 1/4 cup tomato sauce and bake for 50 minutes.
While meatloaf bakes, boil cauliflower florets in 4 cups of water until fork-tender, about 15 minutes. Drain cauliflower and transfer to the food processor along with ghee, chives, garlic, and sea salt. Blend until smooth.
Heat ghee over medium heat in a medium skillet for 2 minutes. Add broccoli and sauté for 6 minutes, turning once.
Cool meatloaf at room temperature for 5 minutes before slicing. Serve alongside mashed cauliflower and broccoli with extra tomato sauce.