Heat 2 tablespoons of the oil in a pan set over a medium-high heat and cook the beef for 3–4 minutes, stirring occasionally, until browned and just cooked through. Remove from the pan with a slotted spoon and set aside. Return the pan to the heat.
Add the remaining oil to the pan and cook the pepper, onion and sweet potato for 5–6 minutes, stirring frequently, until lightly coloured and softened.
Stir the balti sauce into the pan with the tomato wedges, then reduce the heat, cover and simmer gently for about 15 minutes or until the vegetables are tender and the sauce has thickened slightly.
Return the beef to the pan, add the spinach and stir over the heat for 1–2 minutes until the beef is hot and the spinach has wilted. Serve immediately.