Prepare the marinade by mincing the garlic and chopping the fresh herbs. In a small bowl, combine the minced garlic, herbs, 1 teaspoon olive oil, salt, and pepper.
Place the sirloin steak in a shallow dish and rub the marinade all over. Allow it to come to room temperature and marinate for at least 15 minutes.
Preheat the grill to medium-high heat.
Meanwhile, preheat your oven to 425°F. Dice the yellow potato into 1-inch cubes, toss them in 1 teaspoon of olive oil, a pinch of salt, and pepper, and spread on a baking sheet. Roast in the oven for about 20-25 minutes until golden and tender, stirring halfway through.
While the potatoes roast, prepare the mixed vegetables by cutting them into bite-sized pieces. Lightly season with salt, pepper, and a splash of olive oil if desired, then set aside.
Grill the steak for about 4-5 minutes per side or until it reaches your desired doneness.
As soon as the steak is finished, let it rest for a couple of minutes. Then, quickly toss the vegetables in the residual heat or, if preferred, you can briefly roast them in the oven during the last 10 minutes of the potato roasting process.
Plate the grilled steak alongside the roasted potatoes and vegetables. Drizzle any remaining herb marinade over the steak for extra flavor, and serve immediately.