Melt the butter in a skillet over medium heat. Add the garlic and onion. Cook for about a minute, just until fragrant.
Add the broth and the rice to the skillet. Increase the heat to high and bring it to a boil, stirring occasionally. Reduce heat to a low simmer and cover with a lid.
Cook until the rice is tender and the liquid has been absorbed, about 18 minutes. Taste the rice and season with salt, if desired. Fluff with a fork.
Add the mixed vegetables and stir to mix throughout. Remove from heat and let stand for a few minutes to thaw and warm the vegetables. Taste the rice again and add more salt, only if needed. Sprinkle with parsley and serve warm.