Preheat oven to 200°C (180°C fan-forced).
Peel and cut potatoes in thick wedges. Boil or steam them until just tender but not fully cooked.
Place potatoes on a tray, toss with extra virgin olive oil and season with salt. Roast until golden, about 20 minutes.
While the potatoes cook, heat 2 tsp oil in a small pot at low-medium heat. Add garlic and cook until golden, stirring often. Add rice and stir. Add water and a good pinch of salt, lower heat to minimum and cook covered until all the water has been absorbed.
Heat a wok or pan as hot as your stove allows. Add oil, let heat up and add beef.
Brown beef on all sides, add garlic and onion, cook stirring (or flipping the wok or pan) for a minute or two.
Add tomatoes, sauce and chillies if using, season with pepper, mix well and turn off heat.
Serve lomo saltado with potatoes, rice and a side salad. Garnish with chopped coriander or green onion.