Cook the rice ahead of time according to package directions until fluffy. Measure out 3 cups and allow it to cool completely for best texture.
Prepare all vegetables by chopping the onion and carrots. Set aside the peas and edamame.
In a small bowl, whisk together the soy sauce, vinegar, and sugar until fully dissolved.
Heat the vegan butter in a wok or large skillet over high heat. Once hot, add the chopped onion and sauté for about 2 minutes until softened and lightly translucent.
Add the carrots, peas, and edamame. Stir-fry for another 2 minutes until the vegetables are heated through.
Add the cooked rice and pour in the sauce mixture. Stir-fry for 2–3 minutes, breaking up any rice clumps and coating everything evenly.
Remove from heat and serve immediately. Garnish with furikake-style seasoning and green onions if desired.