In a medium saucepan, combine the rinsed quinoa and water. Bring to a boil over high heat.
Once boiling, reduce heat to low, cover, and simmer for 15 minutes or until the quinoa is tender and water is absorbed.
Remove from heat and fluff the quinoa with a fork. Set aside.
Heat the vegetable oil in a large skillet or wok over medium-high heat.
Add the ground beef and cook, breaking it apart with a spatula, until browned and cooked through, about 5 minutes.
Add the diced onion and minced garlic to the skillet with the beef. Cook for 2-3 minutes until the onion is translucent and fragrant.
Add the chopped broccoli florets to the skillet and stir-fry for 4-5 minutes until the broccoli is tender-crisp.
Push the beef and broccoli mixture to one side of the skillet. Pour the beaten eggs into the empty side and scramble until fully cooked, about 1-2 minutes.
Combine the scrambled eggs with the beef and broccoli mixture.
Add the cooked quinoa to the skillet and stir to combine all ingredients evenly.
Pour in the soy sauce, oyster sauce, and sesame oil. Stir well to coat the mixture.
Season with ground black pepper and red pepper flakes. Stir to distribute the seasonings.
Cook for an additional 2-3 minutes, stirring frequently, until everything is heated through.
Remove from heat and garnish with sliced green onions before serving.