Make the yum yum sauce by mixing mayo and ketchup in a bowl. Set aside.

In a skillet over medium-high heat, melt 1 tablespoon of butter. Add shrimp and cook until pink, about 1 minute per side. Add 2 tablespoons of soy sauce; set aside.

Sauté chopped onion and zucchini in another tablespoon of butter for about 4-5 minutes. Add another 2 tablespoons of soy sauce.

Scramble an egg in the skillet with the remaining butter, then add cooled rice and frozen peas and carrots. Stir-fry for 2-3 minutes and mix in the last 2 tablespoons of soy sauce.

Serve by layering rice mixture in bowls topped with sautéed veggies and shrimp, drizzling with yum yum sauce.