Adjust rack to top position and preheat oven to 425 degrees. Wash and dry produce.

Cut potatoes into ½-inch-thick wedges. Toss on a baking sheet with a drizzle of oil, oregano, half the garlic powder (you’ll use the rest later), salt, and pepper. Roast on top rack until browned and tender, 20-25 minutes.

Halve, peel, and cut half the onion (whole onion for 4 servings) into ½-inch wedges. Cut tomato into ½-inch wedges. Roughly chop cilantro.

In a small pot, combine rice, ¾ cup water (1½ cups for 4 servings), and a pinch of salt. Bring to a boil, then cover and reduce to a low simmer. Cook until rice is tender, 15-18 minutes. Keep covered off heat until ready to serve.

While rice cooks, pat steak* dry with paper towels; slice into 1-by-3-inch strips (the strips don’t need to be perfect—a rough 1-by-3 inches is fine!).

In a medium bowl, combine cornstarch, half the cumin (all for 4 servings), remaining garlic powder, salt, and pepper. Add steak and toss until coated.

Heat a drizzle of oil in a large pan over medium-high heat. Add steak and cook, tossing occasionally, until a crust forms, 4-6 minutes (steak will finish cooking in the next step). Turn off heat; transfer to a plate. Wipe out pan.

Heat another drizzle of oil in pan used for steak over medium heat. Add onion wedges and tomato; cook, stirring occasionally, until slightly tender, 4-6 minutes.

Add steak, soy sauce, Sriracha, ⅓ cup water, 2 tsp vinegar, and ¼ tsp sugar (⅔ cup water, 4 tsp vinegar, and ½ tsp sugar for 4 servings). (Save remaining vinegar for another use.) Cook, stirring constantly, until sauce has thickened and steak is cooked through, 1-3 minutes.

Taste and season with salt and pepper if desired.

Fluff rice with a fork; stir in 1 TBSP butter (2 TBSP for 4 servings).

Divide rice and potatoes between plates in separate sections. Top potatoes with steak stir-fry. Garnish with cilantro and serve.