Preheat your oven to 400°F (200°C).
Chop the beef top sirloin into 1-inch cubes and pat them dry with a paper towel to ensure a good sear.
Prepare the vegetables by halving the Brussels sprouts and dicing the red potato and carrots into small, uniform pieces.
Heat the avocado oil in a large cast-iron skillet or oven-safe pan over medium-high heat.
Add the beef cubes to the skillet and sear for 2-3 minutes until a brown crust forms on all sides, then remove the beef and set it aside.
In the same skillet, add the potatoes, carrots, and Brussels sprouts, sautéing for 5 minutes until the edges begin to soften.
Stir in the minced garlic, fresh rosemary, fresh thyme, sea salt, and black pepper, tossing to coat the vegetables.
Return the seared beef to the pan and stir to combine everything evenly.
Transfer the skillet to the oven and roast for 12-15 minutes until the vegetables are tender and the beef is cooked to your preference.
Remove from the oven and serve immediately while the herbs are aromatic and the beef is juicy.