Place the skillet over medium-high heat and add the remaining 3 tablespoons olive oil, the scallion whites and garlic. Cook, stirring, until the garlic sizzles, about 30 seconds. Stir in the rice, season with salt and pepper and spread into an even layer. Cook until slightly browned, 3 to 4 minutes. Stir and cook for 3 minutes more. Push the rice to one side of the pan; add the eggs, season with salt and cook, scrambling, until set, 1 to 2 minutes. Stir the eggs into the rice, then add the shrimp mixture, peas and carrots and scallion greens and cook, stirring, until heated through.