Prepare the Shrimp
Pat shrimp dry with paper towels and season lightly with salt and pepper on both sides. This ensures the shrimp will sear properly rather than steam. Let them rest while you prepare your cooking surface, allowing the seasonings to adhere to the shrimp.
Cook the Shrimp
Heat grapeseed oil in a large skillet or wok over medium-high heat. Add 2 tablespoons of butter and let it melt completely. Add the seasoned shrimp in a single layer and cook for about 3 minutes total, flipping halfway through, until they turn pink and opaque. Be careful not to overcook them. Remove the cooked shrimp to a plate and set aside.
Deglaze the Pan
Pour mirin into the hot pan to deglaze, using a wooden spoon to scrape up any browned bits from the bottom. This step is crucial as it incorporates all the flavorful fond from the shrimp into your dish, creating a more complex flavor profile for your fried rice.
Sauté the Vegetables
Add the remaining 4 tablespoons of butter to the pan. Once melted, add diced onion and cook for 2 minutes until they become translucent and softened. Add the shredded carrots next and continue cooking for an additional 3 minutes until they reach a tender-crisp texture while maintaining their bright color.
Cook the Eggs
Reduce heat to medium and push the vegetables to one side of the pan, creating a well in the center. Add sesame oil to the well, then pour in the beaten eggs. Scramble them gently in the center until they begin to set, then gradually incorporate them with the vegetables, cooking for about 1 minute until the eggs are fully cooked but still soft.
Add Rice and Seasonings
Stir in the cooked rice, breaking up any clumps with your spatula. Day-old rice works best as it's drier and won't become mushy. Season with salt, pepper, and garlic powder, distributing them evenly. Pour the soy sauce and oyster sauce over the rice and stir constantly until the rice takes on a uniform golden-brown color, about 3-4 minutes.
Incorporate Frozen Vegetables
Add the frozen peas and corn directly to the hot rice mixture. The residual heat will quickly defrost them. Continue stirring for 2-3 minutes until these vegetables are heated through and tender, adding vibrant color and sweetness to the dish.
Combine and Serve
Return the cooked shrimp to the pan and gently fold everything together for 1 minute, just enough to heat the shrimp through without overcooking them. Remove from heat, garnish generously with chopped green onions, and serve immediately while hot for the best flavor and texture.