Add diced potatoes to cold salted water. Bring to a simmer and cook for 5 minutes.
Drain and let potatoes steam dry. Season and spray lightly with oil.
Air fry at 200°C for 20 to 25 minutes or bake at 220°C for 25 to 30 minutes.
Season steak with spices and sear on high heat for 30 seconds to 1 minute per side.
Remove steak and sauté onions and peppers in the same pan.
In a separate pan, combine milk, cheese slices, and seasonings. Simmer until smooth and thick.
Assemble potatoes, steak, and veggies. Drizzle with cheese sauce and serve or store.