In a large pot of boiling salted water, cook potatoes until parboiled for 10-12 minutes; drain well.
Arrange steak, potatoes, broccoli, bell pepper, and onion on a large sheet pan. In a small bowl, whisk the garlic, olive oil, Italian seasoning and salt + pepper. Brush the mixture on the steak and veggies.
Place into the oven in the upper-center rack and broil until the steak is browned and charred at the edges and the veggies are lightly charred, about 4-5 minutes per side, flipping once, for medium doneness.
Notes
*substitute small baby potatoes with regular potatoes cut into large chunks.