Prepare the beef mixture. In a large bowl, combine the ground beef, onion powder, garlic powder, beef powder, black pepper, breadcrumbs, eggs, and salt to taste. Mix by hand or with a stand mixer until just combined.
Shape the patties. Scoop handfuls of the mixture and shape into evenly sized burger patties.
Cook the patties. Heat a little cooking oil in a frying pan or grill pan over medium heat. Cook a small test patty first and adjust the seasoning if needed. Fry the remaining patties until browned on both sides and cooked through. Set aside.
Sauté the garlic. Heat a little cooking oil in a pot over medium heat. Add the minced garlic and sauté until fragrant and lightly golden. Remove the garlic and set aside for garnish.
Save the garlic-infused oil. Carefully transfer most of the garlic-infused oil to a heat-safe container, leaving only a thin coating in the pot. Let the reserved oil cool and refrigerate promptly for use in other dishes.
Make the roux. Melt the salted butter in the same pot. Add the all-purpose flour and stir continuously for 1–2 minutes until a smooth roux forms.
Make the gravy. Add the onion powder, garlic powder, beef powder, and black pepper. Gradually pour in the water while stirring or whisking to prevent lumps. Simmer until the gravy starts to thicken. Optional: For a richer, smoother gravy, turn the heat to low or off and stir in an additional ½–1 tablespoon of butter until completely melted and incorporated.
Add the mushrooms. Stir in the sliced brown mushrooms and simmer until tender. Add more water if the gravy becomes too thick, then taste and adjust the salt as needed.
Serve. Arrange the cooked burger patties on a serving plate and spoon the mushroom gravy over them. Top with the reserved sautéed garlic and chopped green onions. Serve with hot steamed white rice.
