Flake leftover salmon into small chunks with a fork. Set aside.
Heat 1/2 tablespoon butter in a medium skillet or wok over medium-high heat. Add yellow onion and cook, until translucent, about 3-4 minutes. Add minced garlic and saute until fragrant, about 2 minutes.
Add the leftover rice in an even layer. Cook, without stirring, 2 to 3 minutes, or until the bottom becomes slightly crispy. Then add the cauliflower rice, frozen peas and carrots, continue to cook, stirring occasionally, 2 to 3 minutes, or until combined.
With a spoon or spatula, push the rice and veggie mixture to one side of the skillet. Crack 2 eggs onto the other side of the skillet. Cook, constantly stirring the egg, until cooked through. Mix the rice, cauliflower and egg to thoroughly combine. Stir in the tamari sauce and sesame oil.
Gently fold in the flaked salmon and toss. Serve immediately garnished with scallion greens and sesame seeds.